NREL/CP-540-46570.Posted with permission. 

Presented at the 2009 SAE Powertrain, Fuels, and 

Lubricants Meeting, 2-4 November 2009, San Antonio, Texas 2009-01-2723 

Effects of Mid-Level Ethanol Blends on Conventional Vehicle Emissions 

Keith Knoll 

National Renewable Energy Laboratory 

Brian West, Shean Huff, John Thomas 

Oak Ridge National Laboratory 

John Orban, Cynthia Cooper 

Battelle Memorial Institute 

ABSTRACT 

Tests were conducted during 2008 on 16 late-model, 

conventional vehicles (1999 through 2007) to determine 

short-term effects of mid-level ethanol blends on 

performance and emissions. Vehicle odometer readings 

ranged from 10,000 to 100,000 miles, and all vehicles 

conformed to federal emissions requirements for their 

federal certification level. The LA92 drive cycle, also 

known as the Unified Cycle, was used for testing as it 

was considered to more accurately represent real-world 

acceleration rates and speeds than the Federal Test 

Procedure (FTP) used for emissions certification testing. 

Test fuels were splash-blends of up to 20 volume 

percent ethanol with federal certification gasoline. Both 

regulated and unregulated air-toxic emissions were 

measured. 

For the aggregate 16-vehicle fleet, increasing ethanol 

content resulted in reductions in average composite 

emissions of both NMHC and CO and increases in 

average emissions of ethanol and aldehydes. Changes 

in average composite emissions of NMOG and NOX 

were not statistically significant. By segregating the 

vehicle fleet according to power-enrichment fueling 

strategy, a better understanding of ethanol fuel-effect on 

emissions was realized. Vehicles found to apply longterm fuel trim (LTFT) to power-enrichment fueling 

showed no statistically significant fuel effect on NMOG, 

NMHC, CO or NOX. For vehicles found to not apply 

LTFT to power-enrichment, statistically significant 

reductions in NMHC and CO were observed, as was a 

statistically significant increase in NOX emissions. 

Effects of ethanol on NMOG and NMHC emissions were 

found to also be influenced by power-to-weight ratio, 

while the effects on NOX emissions were found to be 

influenced by engine displacement. 

INTRODUCTION 

The United States’ Energy Independence and Security 

Act (EISA) of 2007 calls on the nation to significantly 

increase its use of renewable fuels to meet its 

transportation energy needs.1

 The law establishes a new 

renewable fuel standard (RFS) that requires 36 billion 

gallons of renewable fuel to be used in the on-road 

vehicle fleet by 2022. Given that ethanol is the most 

widely used renewable fuel in the United States and 

production is expected to grow steadily over the next 

several years, ethanol—both from corn and from 

cellulosic feedstocks—will likely make up a significant 

portion of the new renewable fuel requirements. The 

vast majority of ethanol currently used in the United 

States is blended with gasoline to create E10—gasoline 

with up to 10 volume percent (vol. %) ethanol. The 

remaining ethanol is sold in the form of E85, a gasoline 

blend with as much as 85 vol. % ethanol that can be 

used only in flexible-fuel vehicles (FFVs). Consumption 

of E85 is currently limited by both the size of the flex-fuel 

vehicle fleet and the number of E85 fueling stations. 

While U.S. automakers have committed to significantly 

1
 

 

 

 

ramping up production of FFVs, only about 7% of the 

existing U.S. fleet is replaced each year. That means a 

significant number of the non-FFVs in use today will 

remain in the vehicle fleet for many years to come. 

In light of projected growth in ethanol production, as well 

as the new RFS, most analysts agree that the E10 

market will be saturated within the next few years, 

possibly as soon as 2010. Although the U.S. Department 

of Energy (DOE) remains committed to expanding the 

E85 infrastructure, that market will not be able to absorb 

projected volumes of ethanol in the near term. Given this 

reality, DOE and others have begun assessing the 

viability of using mid-level ethanol blends (blends of 

gasoline with up to 20 vol. % ethanol) in conventional 

vehicles as one way to potentially accommodate growing 

volumes of ethanol, thereby displacing petroleum and 

helping the country comply with EISA. 

BACKGROUND 

In summer 2007, DOE initiated a test program to assess 

the potential impacts of mid-level ethanol blends on 

typical vehicles (non-FFVs) and other engines that rely 

on gasoline. The test program focuses specifically on the 

effects of E15 and E20, gasoline blended with 15% and 

20% ethanol, but it includes both E0 (gasoline) and E10 

as baseline fuels. Through a wide range of experimental 

activities, DOE is working with partners to evaluate the 

effects of these mid-level ethanol blends on a variety of 

potentially affected equipment. 

Before designing the test program, a literature search 

was conducted indicating that insufficient data existed to 

predict the impacts of these fuels on current U.S. 

vehicles and engines.2

 A study conducted by EPA in 

1995 evaluated near-term effects of mid-level ethanol 

blends (up to 40 vol. % ethanol) on U.S. vehicle fleet 

emissions.3

 Tests were limited to six vehicle models and 

included only 1990 and 1992 model years. All vehicles 

were equipped with fuel injection, 3-way catalysts and 

closed-loop fuel control. All testing was conducted using 

the U.S. Environmental Protection Agency’s (EPA’s) 

Federal Test Procedure (FTP) certification drive cycle. 

Results of the EPA study showed that for these vehicles, 

as ethanol content in the fuel was increased, 

hydrocarbons (HC) and carbon monoxide (CO) 

emissions were reduced and oxides of nitrogen (NOX) 

emissions were increased. Given the age of the vehicles 

included, however, these results may not be relevant to 

the current U.S. vehicle fleet. Advances in engine fuel 

control and catalyst technology driven by progressively 

more stringent emission requirements (including more 

aggressive certification cycles such as the US06) have 

likely altered the effects of ethanol on vehicle tailpipe 

emissions. More recently, the Orbital Engine Company 

conducted a mid-level ethanol blends study for 

Environment Australia.4

 Five vehicle pairs from model 

years 2001 and 2002 were evaluated over 50,000 miles 

using unleaded gasoline and E20. Orbital showed 

increased emissions due to catalyst deterioration over 

the 50,000-mile interval for most vehicles included in its 

study when aged with E20. As noted previously,2 

however, vehicles included in the Orbital study likely had 

different fueling calibrations and catalyst formulations 

than those used in U.S. vehicles since they were 

intended for the Australian market. Consequently, 

relevance to the U.S. vehicle fleet is not clear. The 

Coordinating Research Council (CRC) conducted a 

literature review of fuel-effect studies on vehicle 

emissions as well, and results were published in 2008.5 

While this review provides no information on mid-level 

ethanol blend effects on late-model U.S. vehicles, it does 

provide an excellent context for comparing other fuel 

composition effects on vehicle emissions. 

APPROACH 

Vehicle testing was conducted simultaneously at three 

separate emissions laboratories; Oak Ridge National 

Laboratory (ORNL) in Oak Ridge, TN; Transportation 

Research Center (TRC) in East Liberty, OH; and the 

Colorado Department of Public Health and Environment 

(CDPHE) in Aurora, CO. Testing at all sites was 

conducted at a nominal temperature of 75°F. CDPHE 

also conducted testing at 50°F; however, those results 

are not presented here. 

EMISSIONS MEASUREMENT AND VEHICLE 

INSTRUMENTATION − All laboratories measured 

emissions via full-flow dilution per Code of Federal 

Regulations (CFR) 40 part 86 guidelines. Concentrations 

of CO, NOX, total hydrocarbons (THC), methane (CH4), 

and carbon dioxide (CO2) were measured by 

conventional analyzers. Corrections were applied to 

flame ionization detector (FID) measurements of 

hydrocarbons due to the presence of ethanol and 

aldehydes, per California’s Non-Methane Organic Gas 

Test Procedure.6

 All available data from each vehicle’s 

Engine Control Unit (ECU), such as long- and short-term 

fuel trim values, engine and vehicle speed, and intake 

manifold pressure, were collected at CDPHE and ORNL 

via the Assembly Line Diagnostic Link (ALDL). Fuel trim 

data were also acquired during a two-minute idle period 

following each LA92 drive cycle execution as a quick 

check on fuel adaptation. Additional details regarding 

emissions analyzers and chassis dynamometer 

equipment used at each test lab are contained in the 

National Renewable Energy Laboratory (NREL)/ORNL 

report.7 

All labs sampled aldehydes (including formaldehyde and 

acetaldehyde) using dilution tunnel sample taps with gas 

drawn through dinitrophenylhydrazine- (DNPH)-treated 

silica gel cartridges at a rate of approximately 1 L/min.8 

DNPH cartridges were then post-processed by eluting 

with acetonitrile and analyzing by high-performance 

liquid chromatography. These oxygenated compounds 

are reactive in the atmosphere and must be included 

2
when calculating nonmethane organic gas (NMOG) 

emissions. 

Exhaust gas ethanol concentration was measured by all 

laboratories using the Innova Photoacoustic Multi-gas 

Analyzer supplied by California Analytical Instruments. 

This method, developed and documented by Loo and 

Parker9

 and now accepted by EPA, was used to batch 

sample individual phase emissions for ethanol 

concentration. Because this method includes the 

coupled effects of other gas species on ethanol 

measurement, the instrument must be calibrated and 

configured to measure these interfering species. 

Consequently, appropriate optical filters must be 

installed and calibrated to measure interference gases 

such as water vapor, ammonia, and CO2, and gas 

sampling and interference corrections must be enabled 

in the instrument during operation. 

Unfortunately, for the data acquired at TRC using two 

new instruments, those interference measurements were 

not properly included, so there were errors in 

measurement of ethanol in the exhaust. At ORNL, 

ethanol measurements were near the detection limit of 

the Innova setup. This problem was exacerbated by the 

apparent “hang up” of ethanol in the sample lines—a 

common problem for gas phase ethanol sampling. 

Consequently, estimates of ethanol gas concentrations 

for the six vehicles tested at TRC and the four vehicles 

tested at ORNL were based on volume percent ethanol 

in the gasoline and measured THC emissions. This 

estimation method was developed using exhaust ethanol 

data acquired from the NREL/CDPHE dataset at both 

50° and 75°F. This dataset included 24 points—three 

vehicles, four fuels, and two temperatures. These data 

showed strong correlation with a coefficient of 

determination, R2

, of greater than 95%. While not as 

desirable as direct ethanol measurement, this method 

was believed to provide the best estimate of ethanol 

concentration in the exhaust for the purposes of NMOG 

calculation. 

A wide-range universal exhaust gas oxygen sensor 

(UEGO) was used on each vehicle to record the realtime fuel:air equivalence ratio. This information was 

necessary to understand how each test vehicle’s fuel 

control system responded to the oxygenated fuels. 

EXHAUST AND CATALYST TEMPERATURE 

MEASUREMENTS − Each vehicle’s exhaust system 

was modified to allow measurement of exhaust gas 

temperature, catalyst core temperature and exhaust 

fuel:air ratio. Several key exhaust temperatures were 

measured on each vehicle at the following locations. 

•	 Engine-out or pre-catalyst, measured using a 1/8 in. 

thermocouple located upstream of the catalyst core 

or in the exhaust manifold. 

•	 Catalyst core, measured using a 1/16 in. or 1/8 in. 

thermocouple installed directly into the center of the 

catalyst core at 1 in. from the leading face. 

•	 Between first and second catalysts (for vehicles with 

dual catalyst configuration), measured using a 

1/8 in. thermocouple located between catalysts. 

•	 Second catalyst core (for vehicles with dual catalyst 

configuration), measured using a 1/16 in. or 1/8 in. 

thermocouple installed directly into the center of the 

second catalyst core at 1 in. from the leading face. 

•	 Catalyst outlet, measured using a 1/8 in. 

thermocouple located 6 in. downstream of the 

catalyst outlet. 

Each vehicle’s exhaust system was removed so that 

thermocouples, UEGO ports, and exhaust sample ports 

could be installed. Figure 1 shows an example exhaust 

system modified for this program from a 4-cylinder 

Toyota Camry. Only the exhaust manifold and first 

catalyst are shown. Similar temperature and sample 

ports were installed in the second catalyst and outlet 

pipe. 

Factory EGO 

Added UEGO 

2.54 cm 

Added Engine-out sample Added Thermocouple 

Figure 1: Typical Instrumentation of Vehicle Exhaust 

System 

VEHICLE SELECTION − A database of U.S. registered 

vehicles was purchased from R. L. Polk & Co. to 

characterize the population of light-duty vehicles in the 

U.S. fleet in 2007. 

Table 1 shows the number of gasoline-powered (nonFFV) registered vehicles by model year period, 

manufacturer, and number of cylinders. Vehicles were 

selected from this database based primarily on sales 

volume, but also considering the vehicle manufacturer 

and engine configuration (number of cylinders and 

displacement). 

Model year periods were generally defined to 

correspond to different regulatory periods. For the 

purposes of this study, vehicles were categorized by 

model year into four basic emission level groups. 

3
 

 

 

 

 

 

 

 

 

 

 

 

 

•	 Tier 0, Pre-1996: Tier 0 gaseous emissions 

standards were in force from 1981 through 1993 

(although not denoted Tier 0 until 1987). These 

standards were phased out from 1994 through 1996. 

•	 Tier 1, 1996 through 1999: Tier 1 emissions 

standards were phased in from 1994 through 1996 

with full compliance required in 1996. 

•	 Tier 2 Transitional, 2000 through 2004: The National 

Low Emission Vehicle program began transition to 

Tier 2 emissions levels from 2000 through 2004. 

•	 Tier 2, 2004 through 2007: Tier 2 emissions 

standards were phased in for light-duty passenger 

vehicles beginning in 2004, with full compliance 

required in 2007. 

Table 1: Number of Registered Gasoline-Powered 

Vehicles in the United States, January 2007 (thousands) 

Model 

Year Mfr Number of Cylinders Total 4 6 8 Other 

Pre-1996 

(Tier 0 / 

older) 

All 25,948 34,597 16,512 1,573 78,630 

1996 – 

1999 

(Tier 1) 

Chrysler 1,338 3,943 1,584 45 6,910 

Ford 1,894 5,100 4,021 100 11,116 

GM 3,421 7,090 3,851 44 14,406 

Honda 2,581 540 – 35 3,157 

Nissan 1,146 914 28 0 2,088 

Toyota 2,492 1,438 130 1 4,061 

VW 542 188 6 0 737 

Other 2,228 1,206 294 278 4,006 

Subtotal 15,642 20,420 9,915 504 46,481 

2000 – 

2004 

(Tier 2 

 Trans) 

Chrysler 1,788 4,191 2,445 25 8,449 

Ford 1,586 5,603 5,300 256 12,744 

GM 3,474 9,894 5,996 88 19,452 

Honda 3,671 2,154 – 0 5,825 

Nissan 1,293 2,045 163 0 3,501 

Toyota 3,778 3,174 1,001 – 7,953 

VW 1,309 474 55 0 1,838 

Other 4,466 4,139 784 447 9,836 

Subtotal: 21,366 31,673 15,743 816 69,598 

2005 – 

2007 

(Tier 2) 

Chrysler 767 2,528 1,071 8 4,373 

Ford 715 2,095 1,934 43 4,786 

GM 1,652 3,589 2,265 273 7,779 

Honda 1,752 1,273 – – 3,025 

Nissan 872 1,088 238 – 2,199 

Toyota 2,457 1,935 499 – 4,892 

VW 288 91 41 181 601 

Other 1,956 2,000 425 278 4,659 

Subtotal: 10,458 14,599 6,474 782 32,313 

Grand Total: 73,414 101,289 48,645 3,675 227,022 

Vehicles were selected to meet several analysis 

objectives. Of the initial 11 vehicles, three pairs were 

selected to represent a range of engine sizes and 

manufacturers, with each pair consisting of a 2003 and a 

2007 vehicle from the same manufacturer and similar 

engine configuration. The vehicle pairs were chosen to 

evaluate the effect of ethanol during the progression in 

emissions control technology from transitional Tier 2 to 

full Tier 2 compliance. 

•	 2003 and 2007 Toyota Camry 2.4L I4 

•	 2003 and 2007 GM LeSabre/Lucerne 3.8L V6 

•	 2003 and 2007 Ford F150 5.4L V8 

Five additional vehicles were selected based on sales 

volume data; however, some consideration was also 

given to vehicles that complemented those selected for 

EPA’s EPAct (Energy Policy Act) study, which involved a 

similar test protocol.10 

•	 2003 Ford Taurus 3.0L V6 

•	 2003 Nissan Altima 3.5L V6 

•	 2007 Honda Accord 2.4L I4 

•	 2007 Chrysler Town & Country 3.3L V6 

•	 2007 GM Silverado 4.8L V8 

Following this initial selection of 11 vehicles, a second 

set of vehicles was selected using information from auto 

manufacturers concerning specific models that were 

most likely to be sensitive to increased ethanol content 

in gasoline,11 while also considering sales volumes. 

•	 1999 Honda Civic 

•	 2004 VW Golf GTI 

•	 1999 Ford Crown Victoria 

• 1999 Toyota Corolla 

•	 2001 Chrysler PT Cruiser 

A summary of all vehicles selected for testing is included 

in Table 2. This table contains information about each 

vehicle, including odometer reading at start of test, 

engine family, and applicable emissions standard. 

Table 2: Test Vehicle List 

OEM Model MY Eng. Init. 

Odo. 

EPA Engine 

Family 

Emiss’n 

Standard 

Honda Accord 2007 2.4 L I4 11,400 7HNXV02.4KKC Tier 2, 

 Bin 5 

Nissan Altima 2003 3.5 L 

V6 53,300 3NSXV03.5C7A LEV 

Toyota Camry 2003 2.4 L I4 72,800 3TYXV02.4HHA ULEV 

Toyota Camry 2007 2.4 L I4 26,440 7TYXV02.4BEB Tier 2 

 Bin 5 

Honda Civic 1999 1.6 L I4 79,680 XHNXV01.6TA3 Tier 1 

Toyota Corolla 1999 1.8 L I4 96,400 XTYXV01.8XBA Tier 1 

Ford Crown 

Victoria 1999 4.6 L 

V8 50,900 XFMXV04.6VBE ULEV 

Ford F150 2003 5.4 L 

V8 57,000 3MFXT05.4PFB Tier 1 LEV 

Ford F150 2007 5.4 L 

V8 28,600 7FMXT05.44H7 Tier 2 

 Bin 8 

VW Golf GTI 2004 1.8 L 

I4-T 32,900 4ADXV01.8356 Tier 2 

 Bin 8 

GM 

(Buick) LeSabre 2003 3.8 L 

V6 78,000 3GMXV03.8044 Tier 2 

 Bin 8 

GM 

(Buick) Lucerne 2007 3.8 L 

V6 10,000 7GMXV03.9146 Tier 2 

 Bin 5 

Chrysler PT 

Cruiser 2001 2.4 L I4 93,400 1CRXV02.4VD0 NLEV 

GM Silverado 2007 4.8 L 

V8 12,800 7GMXT05.3379 Tier 2 

 Bin 8 

Ford Taurus 2003 3.0 L 

V6 89,600 3FMXV03.0VF3 Tier 2 

 Bin 8 

Chrysler Town & 

Cntry 2007 3.3 L 

V6 35,000 7CRXT03.8NEO Tier 2 

 Bin 5 

Although the 16 vehicles included were not selected “at 

random,” with the exception of the three 1999 modelyear vehicles they are generally representative of the 

population of late-model gasoline-powered vehicles 

4
 

 

(model year 2000 to 2007) that were on the road in early 

2007. In particular, the number of vehicles tested was 

nearly proportional to the population counts for each 

manufacturer, engine size category (number of 

cylinders), and emissions standard period (Transitional 

Tier 2: 2000 through 2004 or Tier 2: 2005 through 2007). 

TEST FUELS − Four fuels of varying ethanol blend level 

were included in this program. Ethanol blend 

concentration levels were specified on a volume-percent 

basis and included 0%, 10%, 15%, and 20% (E0, E10, 

E15, and E20). E0 and E10 were both included as they 

represent legal fuels for sale in the United States. E15 

and E20 represent mid-level blends which may be 

considered for legal sale. 

The E0 test fuel was certification gasoline (Indolene) 

supplied by Gage Products Company. Other fuels were 

splash blends of this E0 fuel with the appropriate 

quantity of fuel-grade ethanol (per ASTM D4806). All fuel 

blending was done by Gage Products, and finished test 

fuels were delivered to each of the test labs. Splash 

blends were used for expediency in this pilot study 

because of the long iterative development process 

required to obtain match-blended fuels. The main 

differences in fuel chemistry between splash-blended 

and match-blended fuels are expected to be vapor 

pressure and hydrocarbon profile, neither of which is 

expected to have a significant effect on the major 

findings of this study. Other ongoing testing within the 

DOE Mid-Level Blends Test Program will validate this 

assertion via testing with match-blended fuels. 

Table 3: Test Fuel Properties 

Test 

Lab Fuel EtOH 

(vol-%) 

DVPE 

(kPa) 

LHV 

(MJ/kg) SG C 

(wt-%) 

H 

(wt-%) 

O 

(wt-%) 

ASTM Method: D5599 D5191 D240 D4052 D5291 D5291 D5599 

NREL / 

CDPHE 

E0 0.0 61.8 43.11 0.746 86.15 13.05 0.00 

E10 9.9 67.6 41.57 0.750 81.84 12.37 3.65 

E15 13.9 66.4 40.64 0.752 80.72 12.68 5.11 

E20 18.6 66.5 39.75 0.754 78.77 12.92 6.79 

ORNL / 

TRC 

E0 0.0 57.9 43.11 0.746 86.83 12.97 0.00 

E10 9.1 65.4 41.51 0.750 82.56 12.62 3.36 

E15 14.4 64.3 40.67 0.752 80.16 12.52 5.27 

E20 19.8 63.6 39.64 0.755 79.66 12.84 7.23 

ANL / 

TRC 

E0 0.0 58.5 43.13 0.746 86.83 12.85 0.00 

E10 9.9 64.4 41.39 0.751 82.29 12.85 3.62 

E15 14.3 64.7 40.50 0.752 80.58 13.41 5.24 

E20 19.6 63.1 39.64 0.755 78.97 12.71 7.17 

Fuels were analyzed by the Fuel Analysis Laboratory at 

Southwest Research Institute. Table 3 provides a partial 

list and summary results of analyses performed. Fuels 

are labeled according to test lab and nominal ethanol 

concentration. The three pickup trucks tested at TRC 

were tested under subcontract with Argonne National 

Laboratory (ANL), while the three passenger cars at 

TRC were tested under subcontract with ORNL and 

used the same fuel as the vehicles tested at ORNL. 

Figure 2 provides distillation properties of the fuels used 

based on an analysis of the NREL fuel set, including 

tabulated values for T10, T50, and T90 for each ethanol 

concentration. 

Although test fuels were expected to be from common 

blend stocks, some differences in fuel properties were 

observed. Fuels were specified to be within 1% of 

nominal ethanol content. Fuels at the NREL test lab 

were found to be slightly below this specification at 13.9 

vol. % ethanol for the E15 fuel and 18.6 vol. % ethanol 

for the E20 fuel. Variations in dry vapor pressure 

equivalent (DVPE) consistent with these ethanol 

variations were observed. While these differences were 

not expected to significantly impact emissions or catalyst 

temperature trends, they should be kept in mind when 

considering the results. 

50 

100 

150 

200 

250 

300 

350 

400 

Temperature (°F) 

E0 E10 E15 E20 

%EtOH T10 (°F) T50 (°F) T90 (°F)

 0 124 220 318

 10 121 197 313

 15 123 166 309

 20 123 164 304 

0 10 20 30 40 50 60 70 80 90 100 

%-Evaporated 

Figure 2: Distillation curves for NREL fuel set 

TEST CYCLE − Emissions were determined using the 

LA92 drive cycle, also known as the Unified Cycle.12 The 

LA92 was chosen based on consultation with staff at 

EPA, the fact that EPA is using the LA92 in the EPAct 

program,10 and the consensus that it is the single drive 

cycle most representative of real-world driving in the 

United States. The LA92 was executed as a three-phase 

test, similar to the FTP cycle, incorporating a 10-minute 

engine-off hot-soak period following phase 2. Phase 3 

was then run as a hot-start replicate of the cold-start 

phase 1. Composite emissions were calculated using the 

same weighting factors as specified for the FTP, per 

CFR requirements. 

Power-enrichment fuel trim strategy for each vehicle was 

determined using a modification of the wide-open throttle 

(WOT) acceleration sulfur purge cycle used in the CRC 

E-60 test program.13 An explanation of powerenrichment fuel trim strategies, why they were 

determined experimentally, and why they are important 

is provided below. The modified cycle used is shown in 

Figure 3. This WOT cycle included a five-minute steady5
 

 

state temperature stabilization period followed by five 

consecutive standing start WOT accelerations from 0 to 

80 mph. The entire protocol was executed twice, and the 

last five WOT accelerations were used for analysis. 

These WOT accelerations were used to force each test 

vehicle into a power-enrichment mode in which openloop fuel trim strategies could be investigated. 

0 

10 

20 

30 

40 

50 

60 

70 

80 

90 

100 

Vehicle Speed (mph)

300 sec @ 55 mph 

60 sec 

@ 

30 mph 

- 15 sec minimum at 80 mph for each cycle 

- 60 sec at 30 mph between excursions 

- 90 sec at idle between excursions for CVS cooldown 

Cycle to be 

executed twice for 

full WOT protocol 

0 200 400 600 800 1000 1200 1400 

Time (sec) 

Figure 3: Modified CRC E-60 WOT drive cycle 

STATISTICAL ANALYSIS − Two types of statistical 

analyses were performed. First, an analysis was 

conducted to determine whether the relative change in 

emissions when using ethanol in the fuel (E10, E15, or 

E20) versus E0, averaged across all vehicles, was 

different from zero. This approach involved calculating 

the change in average measured emissions and fuel 

economy (based on triplicate emissions tests) for each 

vehicle between the fuels containing ethanol (E10, E15, 

and E20) and E0. The relative change for each vehicle 

was obtained by dividing by the average mass emissions 

change with the value for E0. Then a standard t-test was 

performed to determine whether the average change in 

emissions or fuel economy was different from zero at the 

95% confidence level. For this analysis, the 16 tested 

vehicles were treated as a random sample from the 

population of late model vehicles (model years 1999 to 

2007) in the United States in early 2007. Although the 

vehicles were not selected at random, they are generally 

representative of the target population, as discussed 

above. 

Additional analyses were performed to determine if 

certain vehicle or engine characteristics were coupled 

with ethanol fuel effects on emissions. Characteristics 

studied included whether or not the engine applied LTFT 

to power enrichment fueling, power-to-weight ratio, and 

engine displacement. Power-enrichment fuel trim effects 

were first considered alone, followed by a fixed-effect 

linear regression analysis to determine coupling of these 

effects. Fixed effects included fuel type, the three engine 

characteristics (noted above), and all two- and threefactor interactions of each fuel type with one or two 

engine characteristics. This approach permitted testing 

of hypotheses concerning the overall ethanol effects 

(confirming results of the t-tests) as well as whether 

engine characteristics (or combinations of 

characteristics) affected the way in which ethanol 

changed emissions. The model accounted for random 

effects of replicate tests, test set-up, and random 

differences between vehicles. Log transformations were 

applied to the dependent variables, as appropriate, to 

achieve a normal distribution of errors. Analyses were 

performed on the full model (all three engine 

characteristics) as well as various reduced models after 

excluding factors that were not statistically significant. 

VEHICLE PREPARATION AND FUEL ADAPTATION −

Before the start of testing, each vehicle was inspected to 

ensure that all emission control hardware was intact, and 

an ECU scan was conducted to confirm no on-board 

diagnostic (OBDII) faults were present. Each vehicle 

then underwent an initial crankcase oil, oil filter, and air 

filter replacement. Engine oil and filters were per the 

manufacturer’s recommendations. Each vehicle was 

then driven through three US06 drive cycles to stabilize 

the engine oil by eliminating the higher volatility 

components that may have an effect on vehicle 

emissions. Each vehicle’s ECU was again scanned 

before initiation of testing to confirm that there were no 

existing or pending OBDII faults. 

Following initial preparation, vehicles at CDPHE and 

ORNL were tested on the Federal Test Procedure (FTP) 

and Highway Fuel Economy Test protocols to determine 

city and highway fuel economy for comparison to 

published EPA data. Provided these evaluations yielded 

fuel economy results within 10% of EPA database 

values, dynamometer setup and vehicle operation were 

considered to be acceptable. 

Following acquisition and preparation, each vehicle was 

fueled with the appropriate test fuel and adapted 

according to the fuel change protocol described below. 

This fuel change protocol was performed for every fuel 

change throughout the test program. 

1. Drain fuel tank using in-tank fuel pump 

2. Key on for 30 seconds, confirm gauge reading and 

allow vehicle to register new fueling event 

3. Add half tank of new test fuel 

4. Drive 550 (5 minutes at 50 mph), then double US06 

test protocol 

5. Drain tank using in-tank fuel pump 

6. Key on for 30 seconds, confirm gauge reading and 

allow vehicle to register new fueling event 

7. Add half tank of new test fuel 

8. Proceed to emissions test preparation 

The following protocol was executed following fuel 

adaptation and prior to the first emissions test run on 

each fuel. The second and third emissions tests followed 

consecutively without a repeat of the entire preparation 

cycle. 

6
 

 

NOx CO2

- 50.0

- 40.0

- 30.0

- 20.0

- 10.0

0.0

10.0

20.0

30.0

40.0

50.0

1. Vehicle precondition: Drive 550 cycle followed by 

complete LA4 test cycle followed by LA92 test cycle. 

Idle vehicle in Park for 2 minutes following 

completion of LA92, then key off. 

Note: Vehicle precondition was performed following 

overnight vehicle soak at intended test temperature. 

2. Soak vehicle overnight at intended test temperature 

3. Execute LA92 emissions test protocol 

4. Idle vehicle in Park for 2 minutes following each test, 

then key off 

5. Push vehicle (with key in off position) from chassis 

dynamometer to parking/staging area 

6. Perform subsequent vehicle tests at the same test 

temperature with only an LA92 precondition. 

(Previous vehicle test may be used to satisfy 

precondition requirement provided test temperature 

is equivalent.) 

7. Check for existing or pending OBDII fault codes 

following each LA92 test and record result in vehicle 

log book 

At the conclusion of all emissions tests on a given fuel, 

WOT test protocols were conducted as described above. 

The following fuel testing sequence was followed for all 

vehicles. 

1. E0 baseline 

2. E20 

3. E10 

4. E15 

5. E0 repeat 

Initial E0 testing was conducted to obtain a performance 

baseline before the introduction of ethanol blended fuels. 

E20 fuel was tested immediately following E0 to 

precipitate any possible malfunction indicator light (MIL) 

occurrences due to fuel trim effects or clogged filters 

resulting from the increased solvency of E20 fuel. 

Repetition of E0 fueling at the conclusion of emissions 

testing was done to test for any drift in the E0 data over 

time and to see whether the short-term exposure to 

intermediate ethanol blends or the WOT testing might 

have caused any notable change to the emissions 

control system function. 

RESULTS AND DISCUSSION 

EMISSIONS DRIFT ANALYSIS − Emissions drift over 

the duration of the test program was evaluated by 

comparing emissions from the baseline E0 runs with 

results from the repeat E0 runs conducted at the 

conclusion of testing. Drift analysis was intended to 

identify any significant changes in vehicle emissions 

and/or measurement system stability over the course of 

testing as well as provide context for the fuel-effect 

emission trends being analyzed in this study. Emissions 

drift might have occurred as a result of vehicle operation 

using mid-level ethanol blends over numerous drive 

cycles, including LA92, FTP, US06 and the WOT cycle 

described above. Drift in average mass emissions for 

each vehicle was first calculated by comparing averages 

of at least three replicate tests from each test series; E0 

baseline and E0 repeat. Percent changes in mass 

emissions were then calculated and averaged across the 

vehicle fleet. The standard t-test was used, as described 

above, to determine statistically significant trends in the 

observed result. 

Figure 4 shows emissions drift from beginning to end of 

test; error bars indicate 95% confidence intervals. 

Although typical scatter in the data was observed, there 

was no statistically significant drift in NMOG, NMHC, or 

CO emissions. NOX emissions showed a statistically 

significant reduction of about 18%, and CO2 showed a 

reduction of about 2%. No particular vehicle subset 

defined by model year, vehicle miles, or powerenrichment fueling strategy (explained below) appeared 

to have biased these results. 

-50 

-40 

-30 

-20 

-10 

0 

10 

20 

30 

40 

50 

%-Change from Baseline 

Darker shaded bars / asterisk on 

x-axis indicate statistical significance 

(95% Confidence) 

Error bars indicate 

95% confidence 

* * NMOG NMHC NOX CO CO2 

Figure 4: Emissions drift from initial baseline to final 

repeat using E0 fuel 

Reasons for the observed NOX drift are not known; 

however, one possible explanation may be the repetitive 

sulfur purge cycles used throughout this test program. 

Three-way catalysts typically contain base metal 

promoters such as barium;14,15 these materials are 

known to store NOX.

16 These materials also have a high 

affinity for sulfur, and sulfur has been shown to limit 

catalyst effectiveness; the largest effect is on NOX 

performance.16,17,18,19 Catalyst function has been shown 

to recover when sulfur is purged through hot, rich 

operation such as that reached during the repeated 

WOT cycles used in the current study.17,18,19 It may be 

that the vehicles’ exposure to repeated WOT cycles 

resulted in continual improvement of NOX reduction. 

FUEL ADAPTATION ANALYSIS − For a fuel effect 

study, vehicle adaptation to each test fuel is critical. The 

fuel adaptation procedure described above was arrived 

at following careful consideration of previous work in the 

literature as well as consultation with staff at EPA. 

Suitability of the adaptation protocol was validated by 

both analysis of the fuel trim information acquired during 

7
 

 

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7 

test and a review of emissions drift for each vehicle at found to be statistically significant, while lighter shaded 

each fuel-ethanol level. bars indicate results that are not statistically significant. 

Statistical significance is also indicated by an asterisk on 

For the NREL/CDPHE vehicle dataset, fuel trim the x-axis. 

information was acquired continuously during LA92 cycle 

execution and a cycle-average value was determined for 100 

each test. Analysis of this information showed good 

E10 E15 E20 E10 E15 E20 E10 E15 E20 E10 E15 E20 E10 E15 E20 

NMOG NMHC CO NOx Fuel Economy 

Composite Data 

Darker shaded bars / asterisk on x-axis indicate 

statistical significance (95% Confidence) 

* * * * * * * * *

adaptation to each fuel, and fuel trim values correlated 

well with percent ethanol in the fuel. Figure 5 shows a 

typical result. For the ORNL vehicle dataset, fuel trim 

information was acquired during the two-minute idle 

period at the end of each LA92 cycle execution. Again, 

all vehicles showed consistent adaption to each test fuel. 

Considering all fuel trim data acquired, clear 

differentiation in both fuel trim and emissions results 

Percent Change Relative to E0 

50 

0 

-50 

suggested that fuel adaptation on all vehicles was 

adequate to determine fuel-effect variation on emissions. 

-100 

1/29/20081/30/20083/25/20083/26/20083/27/20082/27/20082/28/20082/29/20083/11/20083/12/20083/13/20082/12/20082/13/20082/14/20082/15/2008 

E00-1 E00-2 E10 E15 E20 

Fuel/Test Date 

Avg = - 3.3% 

Avg = - 2.8% 

Avg = 0.7% 

Avg = 2.8% 

Avg = 4.8% 

trends were observed. NMHC and CO both showed -3 

-4 statistically significant reductions with increasing ethanol. -5 For both pollutants, this reduction was on the order of -6 10% to 15% and occurred primarily with a 10% ethanol 

addition. Trends for E15 and E20 were similar to those 

for E10, suggesting minimal if any effect of ethanol blend 

6 

5 

4

Cycle-Average Fuel Trim (%)

Figure 6: Average percent change in emissions and 3 

2 

1 

0 

-1 

fuel economy relative to E0 

While the data showed considerable scatter, some clear -2 

Figure 5: Fuel trim comparison based on three-phase 

LA92 average values 

COMPOSITE EMISSIONS—AGGREGATE VEHICLE 

SET − Ethanol fuel effects on composite vehicle 

emissions were first considered in aggregate for the 16­

vehicle fleet. Composite emissions were calculated as a 

weighted average from the three-phase LA92 cycle, 

computed in the same way that EPA computes the FTP 

from E10 thru E20. Fuel economy showed a statistically 

significant reduction with increasing ethanol content; the 

percent reduction tracked closely with the measured 

energy content of the fuel. NMOG and NOX emissions 

showed no statistically significant trend. Percent change 

in NOX emissions showed the highest scatter of all 

regulated pollutants. There was no correlation between 

percent change in NOX emissions and measured mass 

emissions rates, suggesting that low- and high-emitting 

vehicles were not confounding these results. 

composite emissions for regulatory purposes. Additional 1000 

analyses considering power-enrichment fueling strategy, 

emissions certification level, and phase emissions are 

discussed below. All results are presented in terms of 

statistical significance based on a Student’s t-test. 

“Statistically significant” results are those that can be 

stated with 95% confidence or better. 

Aggregate vehicle emissions trends are shown in 

Figures 6 and 7. Figure 6 shows percent-change in 

regulated tailpipe emissions and fuel economy versus 

E0, while Figure 7 shows the magnitude-change of 

Ethanol Change Relative to E0 (mg/mi)

Aldehyde Change Relative to E0 (%)900 

800 

700 

600 

500 

400 

300 

200 

100 

0 

E10 E15 E20 E10 E15 E20 E10 E15 E20 

Ethanol (x10) Acetaldehyde Formaldehyde 

Darker shaded bars / asterisk on 

x-axis indicate statistical 

significance (95% Confidence) 

Composite Data 

* * * * * * * * * 

ethanol and percent-change of acetaldehyde and -100 

formaldehyde emissions relative to E0. Note that ethanol 

mass emissions are multiplied by 10 to allow for 

common y-axis scaling. Individual data points represent 

individual vehicle results based on averages of at least 

three replicate tests, while bars indicate changes for all 

vehicles on average. Darker shaded bars indicate results 

Figure 7: Average change in composite ethanol and 

aldehyde emissions relative to E0 

8
 

Ethanol and acetaldehyde emissions showed statistically 

significant increases for all ethanol fuels relative to E0. 

Ethanol emissions increased dramatically from E0 to 

E10, and then linearly but to a much lesser degree from 

E10 to E20. Ethanol emissions for E10 were on average 

5.6 mg/mile above E0 values, while average increases 

for E15 and E20 were 6.9 and 8.2 mg/mile, respectively. 

Acetaldehyde emission increases were nearly linear with 

ethanol content and were seen to increase on average 

by about 350% for E20 relative to E0. This effect is 

generally lower than expected based on historical data 

from the literature which would suggest an increase of 

about 600% based on vehicles operating on E85 

(nominally ~80% ethanol assumed).20 For the current 

study, the largest percent increases in acetaldehyde 

were driven entirely by the lower acetaldehyde-emitting 

vehicle set. All vehicles with acetaldehyde increases 

above 500% relative to E0 for any fuel had mass 

emission rates below average (less than 0.7 mg/mile) for 

all fuels tested. On average, acetaldehyde mass 

emissions increased by 0.38, 0.70, and 0.81 mg/mile for 

E10, E15, and E20, respectively, relative to E0. Average 

acetaldehyde emissions for E0 fuel were 0.35 mg/mile. 

Formaldehyde emissions showed statistically significant 

increases for all ethanol concentrations relative to E0, 

but no significant change beyond 10% ethanol addition. 

Fleet average formaldehyde mass emissions rates were 

below 1.0 mg/mile for all fuels tested and below 1.5 

mg/mile for all vehicles except for the oldest, highest 

mileage vehicle in the study which showed formaldehyde 

mass emission rates between 2.5 and 3.5 mg/mile for all 

fuels. 

POWER-ENRICHMENT FUEL TRIM STRATEGIES −

The exhaust gas oxygen (EGO) sensor used on most 

modern vehicles (post-1970s) is a switching type oxygen 

sensor. This type of sensor can determine whether the 

engine is running rich or lean of stoichiometric but does 

not indicate how rich or how lean. Consequently, 

feedback from this sensor can be used only to actively 

adjust for differences in the fuel:air equivalence ratio 

from calibrated values during closed-loop, stoichiometric 

operation. The engine control unit (ECU) typically stores 

such fuel trim information in long-term fuel trim, an array 

of fuel trim values covering a wide range of engine 

operating conditions. LTFT is used to adjust engine 

fueling whenever the engine operates under similar 

operating conditions. In contrast, short-term fuel trim 

(STFT) is used to account for more immediate 

fluctuations in engine fuel trim requirements and is 

assumed to be a single value applied to instantaneous 

operating conditions. LTFT is typically stored in an 

ECU’s nonvolatile memory, meaning it is retained 

following key-off, while STFT is assumed to be stored in 

an ECU’s volatile memory, meaning it is erased following 

each key-off event. Both fuel trim values are intended to 

compensate for variation in vehicle components, such as 

fuel pump pressure, injector flow rate, induction system 

air leaks and various sensor accuracies, both from 

original build and from deterioration over life. Both fuel 

trim values are also intended to compensate for 

variations in fuel composition such as oxygen (or 

ethanol) content. 

During certain operating conditions, such as wide open 

throttle, the ECU switches from closed-loop 

stoichiometric operation to a power-enrichment (i.e., 

fuel-enrichment) mode to reduce exhaust gas 

temperatures and protect both engine and exhaust 

emission control components from thermal damage. This 

enrichment mode is typically open-loop, using a fuel 

enrichment strategy preprogrammed into the ECU. Two 

fuel trim strategies are commonly employed during 

power-enrichment: those that apply LTFT to powerenrichment fueling and those that do not.11 Both powerenrichment strategies have sound technical rationales; 

however, a strategy that does not employ LTFT during 

power enrichment may be more susceptible to engine 

and emission control system damage during high load 

operation because of unanticipated variation in vehicle 

components or fuel composition. 

Polling engine manufacturers and calibrators about the 

fueling strategy used for power enrichment on each 

vehicle led to considerable uncertainty. Calibration 

strategies were variable among engine manufacturers, 

across engine models, and even across model years for 

a specific vehicle model. For legacy vehicles, it was 

often difficult to identify the version of ECU code that 

was installed, since multiple releases over the engine life 

were possible. To further complicate matters, even when 

an engine calibrator was certain of the power-enrichment 

strategy used for a particular vehicle, actual testing 

would not always yield consistent results. Differences 

may have arisen either due to the fuel adaptation 

protocol or the length of time allowed in each adaptation 

cell. Also, coding structure may have prohibited practical 

LTFT learning because power-enrichment was applied 

before adequate time was available for learning during 

closed-loop operation. 

Power-enrichment fuel trim strategies were therefore 

determined experimentally in this study using the WOT 

protocol described previously. To verify proper 

interpretation of power-enrichment strategy, two of the 

vehicles found to not apply LTFT to power-enrichment 

were further tested using EPA’s standard road cycle 

(SRC).21 The SRC is a dynamometer driving schedule 

developed by EPA for vehicle aging and covers a broad 

portion of the engine operating map. Following 

adaptation to E20 fuel, the two vehicles were operated 

over six consecutive SRC cycles and retested according 

to the WOT protocol. Power-enrichment fueling 

strategies for both vehicles remained unchanged. 

Of the 16 vehicles included in the current study, 7 were 

determined to not apply LTFT to power-enrichment 

operation. For each of these vehicles, the decrease in 

fuel:air equivalence ratio observed during powerenrichment at WOT roughly corresponded on a percent 

basis with the increased oxygen content of the fuel. For 

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0

5

1

the balance of vehicles tested (9 of 16), the fuel:air 

equivalence ratio determined during power-enrichment 

operation remained nearly constant as the ethanol 

content in the fuel was increased. 

POWER-ENRICHMENT—DRIVE CYCLE EFFECTS −

The LA92 cycle was chosen for the current test program 

because it was generally considered to be the best 

single drive cycle representative of “real-world” U.S. 

driving behavior. Since the cycle’s development in the 

early 1990s, driving behavior has likely become even 

more aggressive, suggesting that the LA92 may very 

well underpredict typical driving aggressiveness.22 

Positive kinetic energy (PKE) is a parameter often used 

to indicate aggressiveness of various vehicle drive 

cycles.23,24 PKE represents the positive acceleration 

kinetic energy per unit distance and is calculated 

according to the equation 

2 2 ∑(Vfinal −Vinitial)a>0 PKE = distance

where 

Vfinal = final velocity 

Vinitial = initial velocity 

a>0 means for positive accelerations only 

distance = total distance traveled in trip or micro-trip. 

A mean value of PKE can then be calculated by 

averaging the second-by-second values for all positive 

accelerations. To provide a perspective on drive cycle 

aggressiveness, these mean PKE values can be 

compared. For the LA92 cycle, a mean PKE of 0.46 m/s2 

is calculated, whereas for the FTP cycle, the mean PKE 

is 0.36 m/s2

. Based on this metric, the LA92 drive cycle 

is about 29% more aggressive than the FTP drive cycle. 

In closely examining fuel:air ratio during LA92 cycle 

execution, it was determined that vehicles included in 

the current study employed some measure of fuel 

enrichment throughout the drive cycle after initial warmup. Fuel enrichment was considered to have occurred 

when measured lambda was below a threshold value of 

0.95. As a comparison, five of the vehicles included in 

the current study were also operated on the FTP drive 

cycle. Comparison of continuous fuel:air ratio 

measurements for these five vehicles showed increased 

power-enrichment during LA92 operation when 

compared with the FTP drive cycle. Not surprisingly, the 

percent time at power-enrichment depended on the 

vehicle power-to-weight ratio; higher power-to-weight 

ratio resulted in less power enrichment on either cycle. 

For the five vehicles evaluated, LA92 cycle execution 

resulted in about a 25% or greater increase in power 

enrichment relative to FTP cycle execution. Because 

power enrichment is expected to heavily influence drive 

cycle emissions, and in consideration of the clear 

differentiation in power-enrichment fueling strategies 

within the vehicle fleet, the vehicle set was segregated 

according to power-enrichment fueling strategy to 

determine any possible influence on emissions results. 

COMPOSITE EMISSIONS—POWER ENRICHMENT 

FUEL TRIM EFFECTS − Figures 10 and 11 show 

composite vehicle emission trends for the 16-vehicle 

fleet; average values are separated according to powerenrichment fueling strategy. Red and pink shaded bars 

indicate average values for those vehicles determined 

not to apply LTFT to adjust fuel trim during powerenrichment operation, while blue and light blue bars 

indicate average values for those vehicles determined to 

apply LTFT during power enrichment. Darker shaded 

bars indicate statistically significant results at the 95% 

confidence level. Individual data points are included to 

show individual vehicle results based on at least three 

replicate tests. Figure 10 shows regulated emissions and 

fuel economy as a percent change relative to E0. Figure 

11 shows ethanol and aldehyde emissions change 

relative to E0; ethanol is shown as a magnitude change 

while acetaldehyde and formaldehyde are shown as a 

percent-change. As shown in Figure 10, vehicles found 

to apply LTFT to power-enrichment operation showed no 

statistically significant change in NMOG, NMHC, CO or 

NOX emissions for any ethanol content through E20 

relative to E0. 

-100 

-50 

0 

50 

100 

E10 E15 E20 E10 E15 E20 E10 E15 E20 E10 E15 E20 E10 E15 E20 

NMOG NMHC CO NOx Fuel Economy 

Percent Change Relative to E0 

Vehicle does not apply LTFT 

at power-enrichment 

Vehicle does apply LTFT at 

power-enrichment 

Composite 

Data 

Darker shaded bars indicate statistical 

significance (95% Confidence) 

Figure 10: Percent change in composite emissions and 

fuel economy relative to E0 

Those vehicles found not to apply LTFT to power 

enrichment operation showed no statistically significant 

change in NMOG emissions; however, statistically 

significant effects were observed for NMHC, CO, and 

NOX. NMHC and CO both showed statistically significant 

reductions on the order of 20% to 25% relative to E0 for 

all ethanol concentrations (with the exception of NMHC 

at E15, which was determined to not be statistically 

significant). NOX emissions for this vehicle subgroup 

showed a statistically significant increase of about 35% 

for E20 fuel relative to E0. E10 and E15 fuels showed no 

statistically significant NOX effect. Average NOX mass 

10
 

 

 

emission rates were about 0.1 g/mile for all ethanol 

concentrations. Two of the five vehicles with the highest 

percent NOX increases for E20 also had NOX mass 

emissions at or above the average value, suggesting 

these results were not skewed by the lowest emitting 

vehicles. Although mass emissions rates were much 

lower for the vehicles tested here, these trends were 

generally consistent with earlier results found by EPA for 

Tier 0 vehicle effects.3 

As shown in Figure 11, ethanol and acetaldehyde 

emissions exhibited statistically significant increases for 

both vehicle subgroups when compared with E0. 

Vehicles that did not apply LTFT to power-enrichment 

exhibited slightly higher ethanol increases relative to E0 

than did vehicles found to apply LTFT to power 

enrichment. Acetaldehyde increases were roughly 

linearly proportional to ethanol content. Vehicles that 

applied LTFT to power enrichment tended to show 

slightly higher increases in acetaldehyde relative to E0. 

This differentiation in acetaldehyde emissions according 

to power-enrichment fueling strategy was not skewed by 

lower emitting vehicles. Statistically significant 

formaldehyde increases were observed only for vehicles 

that applied LTFT to power-enrichment operation and 

only for E10 and E20 fueling. Formaldehyde increases 

for the vehicle subgroup that applied LTFT to power 

enrichment were on the order of 35% to 45% relative to 

E0 and occurred primarily from E0 to E10. 

-100 

0 

100 

200 

300 

400 

500 

600 

700 

800 

900 

1000 

E10 E15 E20 E10 E15 E20 E10 E15 E20 

Ethanol (x10) Acetaldehyde Formaldehyde 

Ethanol Change Relative to E0 (mg/mi)

Aldehyde Change Relative to E0 (%) 

Composite 

Data 

Vehicle does not apply LTFT 

at power-enrichment 

Vehicle does apply LTFT at 

power-enrichment 

Darker shaded bars indicate 

statistical significance 

(95% Confidence) 

Figure 11: Average change in composite ethanol and 

aldehyde emissions relative to E0 

COMPOSITE EMISSIONS—OTHER ENGINE 

CHARACTERISTIC EFFECTS − Additional analyses 

were performed to determine if differences in certain 

vehicle/engine characteristics influenced the effects of 

ethanol on tailpipe emissions. Three factors were 

included in this analysis: power-enrichment fuel trim 

strategy, power-to-weight ratio, and engine 

displacement. Power-to-weight ratio was calculated 

using published rated power values for each engine and 

equivalent test weights (ETW) for each vehicle (curb 

weight + 300 lbm); units were in hp/lb. 

Fixed-effect analyses were conducted with three 

objectives in mind: 

1. Determine effect of ethanol concentration on 

emissions and fuel economy 

2. Determine if the effect of ethanol on emissions 

varied according to vehicle/engine characteristics 

(i.e., a significant two-way interaction between a 

vehicle/engine characteristic and ethanol 

concentration) 

3. Determine if the effect of ethanol on emissions 

varied with different combinations of vehicle/engine 

characteristics (i.e., a significant three-way 

interaction among two vehicle/engine characteristics 

and ethanol concentration). 

Analyses were performed using the full model (all factors 

included) as well as various reduced models after 

excluding factors that were not statistically significant. 

Consistency of results among different levels of ethanol 

(E20 versus E0, E15 versus E0, and E10 versus E0) 

were considered in evaluating the results. 

Results from this analysis relative to the first objective 

were consistent with findings from the t-test method 

discussed in the previous section. Statistically significant 

results pertaining to the second and third objective are 

discussed below, and shown in Figures 12 through 15. NMOG Relative Change (%) 60 

40 

20 

0 

-20 

-40 

-60 

Vehicle does not apply LTFT 

at power-enrichment 

Vehicle does apply LTFT at 

power-enrichment 

0.03 0.04 0.05 0.06 0.07 

Power-to-Weight Ratio (hp/lbm) 

Figure 12: Change in relative NMOG composite 

emissions with 20% fuel ethanol by LTFT strategy and 

power-to-weight ratio. Interaction of LTFT and power-toweight ratio is statistically significant at the 95% 

confidence level. 

Although there was no statistically significant difference 

in average emissions of NMOG when using various 

levels of ethanol in the fuel, as shown in Figures 6 and 

10, there was a statistically significant three-way 

interaction involving ethanol, power-enrichment fuel trim 

strategy, and power-to-weight ratio. This effect was 

statistically significant (at the 95% confidence level) 

when all three ethanol fuels (E10, E15, and E20) were 

compared with E0. As shown in Figure 12, the relative 

change in NMOG emissions (from E0 to E20) was 

minimal for all vehicles with a power-to-weight ratio 

11
 

60 

between 0.04 and 0.05; however, as the vehicle powerto-weight ratio increased, ethanol tended to produce a 

larger increase in NMOG emissions for vehicles found to 

apply LTFT during power enrichment. For vehicles found 

to not apply LTFT during power enrichment, a 

decreasing trend in NMOG was observed. 

Findings for NMHC were very similar to those for 

NMOG, except (a) there was a statistically significant 

decrease in NMHC emissions averaged across all 

vehicles, as discussed earlier, and (b) the statistical 

significance of the interaction between powerenrichment fuel trim strategy and power-to-weight ratio 

was only marginally significant (at the 90% confidence 

level). Figure 13 shows the relationship between the 

change in NMHC emissions relative to E0 versus powerto-weight ratio for the two vehicle subgroups. 

The effect of power-enrichment fuel trim strategy on the 

relative change in CO emissions was statistically 

significant at the 95% confidence level for all three fuel 

ethanol levels as shown previously in Figure 6. As 

shown in Figure 10 and confirmed in Figure 14, the 

average effect of 20% ethanol on CO emissions was 

negligible for vehicles that applied LTFT at power 

enrichment; however, there was an average of 30 

percent reduction in CO emissions among vehicles that 

did not apply LTFT at power enrichment. Effects of 

engine displacement and power-to-weight ratio (not 

shown) on the change in CO emissions were not 

statistically significant. 

The effect of 20% ethanol on NOX emissions is shown in 

Figure 15. The effect of power-enrichment fuel trim 

strategy on NOX emissions was statistically significant; 

however, there was also a marginally significant (90% 

confidence level) interaction involving displacement. In Vehicle does not apply LTFT 

at power-enrichment 

Vehicle does apply LTFT at 

power-enrichment 

Figure 15: Change in relative composite NOX 

composite emissions with 20% fuel ethanol by LTFT 

particular, there was minimal change in average NOX

Percent NMHC Change Relative to E0 

emissions for vehicles that applied LTFT at power 40 

enrichment; however, relative NOX emissions tended to 20 increase with engine displacement for vehicles that did 

not apply LTFT during power enrichment. Results for the 0 E10 and E15 fuels were not as conclusive. 

-20 100 Vehicle does not apply LTFT 

at power-enrichment 

Vehicle does apply LTFT at 

power-enrichment 

80 

-40 

NOx Relative Change (%) 60 

-60 40

0.03 0.04 0.05 0.06 0.07 

20 Power-to-Weight Ratio (hp/lbm) 

Figure 13: Change in relative NMHC composite 0 

emissions with 20% fuel ethanol by LTFT strategy and -20 

power-to-weight ratio. Interaction of LTFT strategy and -40 

power-to-weight ratio is marginally significant at the 90% -60 confidence level. 

-80 

0 1 2 3 4 5 6 

Displacement (L) 60 Vehicle does not apply LTFT 

at power-enrichment 

Vehicle does apply LTFT at 

power-enrichment 40 

20 

0 

-20 

-40 

-60 

0 1 2 3 4 

Displacement (L) 

Percent CO Change Relative to E0 

strategy and engine displacement. Interaction of LTFT 

strategy and engine displacement is marginally 

significant at the 90% confidence level. 

There was no statistical evidence that engine 

characteristics influence how fuel ethanol content affects 

emissions of ethanol and aldehydes. 

PHASE EMISSIONS ANALYSIS − Individual phase 5 6	 emissions were also considered both for the 16-vehicle 

fleet in aggregate and for the vehicle subgroup split as 

Figure 14: Change in relative CO composite emissions 

with 20% fuel ethanol by LTFT strategy and engine 

displacement. Effect of LTFT strategy is statistically 

significant at the 95% confidence level, whereas effect of 

engine displacement is not statistically significant. 

used above—those that applied LTFT at power 

enrichment and those that did not. As noted above, the 

LA92 was conducted as a three-phase test incorporating 

a 10-minute engine-off hot-soak period following phase 

2. Phase 3 was then run as a hot-start replicate of the 

cold-start phase 1. Figures below focus on the 

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0

1

2

3

4

5

6

 

aggregate vehicle results to maximize statistical 

significance due to the larger sample size. 

Phase 1 emissions for the 16-vehicle fleet are shown in 

Figure 16 using the same graphing methodology as 

described for Figure 6. Comparing Figures 6 and 16, 

generally consistent fuel-effect trends in NMOG, NMHC, 

and CO are observed between composite and phase 1 

results. NMOG emissions showed no statistically 

significant trend with fuel ethanol content; NMHC 

showed a statistically significant reduction of between 

10% and 15% for all fuels relative to E0. CO reductions 

were between 5% and 10%, but they were statistically 

significant only for E10. When phase 1 data were split 

between power-enrichment fuel trim strategy (not 

shown), CO reductions of 15% to 20% were observed 

for vehicles found to not apply LTFT during power 

enrichment. Almost no phase 1 CO change was 

observed for the vehicle subgroup found to apply LTFT 

during power enrichment. Phase 2 results were similar, 

but with reduced statistical significance. 

-100 

-50 

0 

50 

100 

E10 E15 E20 E10 E15 E20 E10 E15 E20 E10 E15 E20 E10 E15 E20 

NMOG NMHC CO NOx Fuel Economy 

Percent Change Relative to E0 

Phase 1 

Data 

* ** * * * ** 

Vehicle does not apply LTFT 

at power-enrichment 

Vehicle does apply LTFT at 

power-enrichment 

Darker shaded bars / astrisk on x-axis indicate 

statistical significance (95% Confidence) 

Figure 16: Percent change in phase 1 emissions and 

fuel economy relative to E0 

generally consistent with composite results, showing no 

statistically significant trends. Phase 3 NOX emissions, 

however, showed statistically significant increases for all 

ethanol fuel concentrations. Increases were between 

65% and 100% relative to E0. Vehicles found to not 

apply LTFT to power-enrichment operation (not shown) 

exhibited the highest NOX emissions increases; results 

for E20 showed a statistically significant 160% increase 

relative to E0. Phase 3 mass emissions rates for NOX 

were about 0.2 g/mile on average—about one-third of 

phase 1 mass emissions rates and about twice the 

composite emissions values. In general, mass emissions 

rates for NOX were still driven by phase 1 values; 

however, the fuel-effect—especially for vehicles found to 

not apply LTFT to power-enrichment—was primarily 

driven by phase 3 results. 

-100 

0 

100 

200 

300 

400 

500 

600 

E10 E15 E20 E10 E15 E20 E10 E15 E20 E10 E15 E20 E10 E15 E20 

NMOG NMHC CO NOx Fuel Economy 

Percent Change Relative to E0 

Vehicle does not apply LTFT 

at power-enrichment 

Vehicle does apply LTFT at 

power-enrichment 

Phase 3 

Data 

* * * * * ** * ** * ** 

Darker shaded bars / asterisk on 

x-axis indicate statistical 

significance (95% Confidence) 

Figure 17: Percent change in phase 3 emissions and 

fuel economy relative to E0 

Ethanol and aldehyde composite emissions trends were 

primarily driven by phase 1 results, both for mass 

emissions rates and fuel-effect results. 

Phase 3 emissions trends, shown in Figure 17, were 

similar to composite results for NMOG, NMHC, and CO, 

though with notable differences in statistical significance. 

NMOG and NMHC both showed statistically significant 

reductions of 15% to 35% for E10 and E20, respectively, 

relative to E0; however, no significant trend for E15 was 

observed. CO showed statistically significant reductions 

of 40% to 50% relative to E0 for all ethanol 

concentrations. Phase 3 mass emissions for NMOG, 

NMHC, and CO were on average about one-fifth to onetenth of the values observed for phase 1. In general, 

NMOG, NMHC, and CO exhibited individual phase 

emissions trends consistent with composite results; 

mass emissions rates were driven primarily by phase 1. 

In contrast, phase 1 NOX emissions trends shown in 

Figure 16 were not consistent with the composite results 

of Figure 6. Phase 1 NOX emission showed reductions 

for E10 and E15 of nearly 10%, and the E15 result was 

statistically significant. Phase 2 NOX emissions were 

CATALYST TEMPERATURE EFFECTS − As expected, 

vehicles that did not apply LTFT to power-enrichment 

conditions were found to exhibit higher catalyst 

temperatures during WOT operation as fuel-ethanol 

content increased. These higher catalyst temperatures 

were expected because of leaner operation during WOT 

for this vehicle subgroup. Vehicles that were found to 

apply LTFT during WOT operation showed no significant 

change in peak catalyst temperature with ethanol 

content. 

Figure 18 shows the average difference in peak catalyst 

temperature for 10%, 15%, and 20% ethanol content 

relative to E0 for the 16-vehicle fleet. For the 7 vehicles 

found to run leaner during power enrichment, a roughly 

linear increase in peak catalyst temperature was 

observed with increasing ethanol content. For E20, peak 

catalyst temperatures were seen to increase on average 

about 30°C relative to those for E0. For the 9 vehicles 

found to apply LTFT to power-enrichment operation, 

average peak catalyst temperatures were found to be 

13
 

 

 

unaffected by ethanol content, but with considerable 

scatter in the data. Catalyst temperatures during closedloop stoichiometric operation were seen to be generally 

lower with increasing ethanol content as a result of the 

cooling effect of ethanol on the combustion process 

(data not shown). Average Temperature Change at WOT (°C) 50 

40 

30 

20 

10 

0 

-10 

-20 

Vehicle DOES apply LFT during power enrichment 

Vehicle DOES NOT apply LFT during power enrichment 

Range bars indicate maximum and minimum observed 

temperature differences for all vehicles tested. 

E10 E15 E20 

Figure 18: Change in catalyst temperature versus fuel 

type for wide-open throttle (WOT) power-enrichment 

conditions. 

Catalyst temperature is important because catalyst 

durability is adversely affected by exposure to higher 

than design temperatures. EPA uses the Arrhenius 

relationship to predict catalyst life for emission control 

system durability compliance.21 According to this 

relationship, temperature has an exponential effect on 

predicted catalyst life. Because the effect of ethanol in 

the current study was either to increase catalyst 

temperature during power-enrichment operation (for one 

vehicle subgroup), or to decrease catalyst temperature 

during normal, closed-loop operation (for all vehicles 

tested), the overall effect of ethanol on a catalyst’s full 

useful life was not clear. A full-useful-life durability study 

is needed to accurately determine such an effect. 

CONCLUSION 

This study quantified the short-term effects of mid-level 

ethanol blends (E0, E10, E15, and E20) on late-model, 

light-duty vehicle emissions and catalyst temperatures. 

The LA92 driving cycle was used for all emissions 

evaluations. Key conclusions are as follows: 

1. For the aggregate vehicle set, increasing the ethanol 

content from 0% to 20% resulted in no significant 

effect on composite NMOG and NOX emissions. 

NMHC and CO emissions were both reduced while 

ethanol and acetaldehyde emissions were both 

increased at all ethanol concentrations. 

Formaldehyde emissions increased at 10% ethanol 

but showed no further increase with increasing 

ethanol content. 

2. Ethanol effects on tailpipe emissions can be 

differentiated according to ECU power-enrichment 

fueling strategy; vehicles that applied LTFT to 

power-enrichment operation and vehicles that did 

not apply LTFT to power-enrichment operation. 

3. Vehicles that applied LTFT to power-enrichment 

operation showed no significant effect of ethanol 

content on LA92 composite emissions for NMOG, 

NMHC, CO, or NOX. Composite emissions of 

ethanol, acetaldehyde and formaldehyde, however, 

increased with increasing ethanol content. 

4. Vehicles that did not apply LTFT to powerenrichment operation showed reductions in NMHC 

and CO and increases in NOX, ethanol, and 

acetaldehyde with increasing ethanol content. 

Formaldehyde emissions were mostly unchanged. 

5. NMOG and NMHC emissions showed a coupled 

effect with power-enrichment fuel trim strategy and 

vehicle power-to-weight ratio. As power-to-weight 

ratio increased, NMOG and NMHC emissions 

increased with increasing ethanol for vehicles that 

applied LTFT to power enrichment, while these 

emissions decreased for vehicles that did not apply 

LTFT to power enrichment. 

6. NOX emissions showed a coupled effect with powerenrichment fuel trim strategy and vehicle engine 

displacement. As engine displacement increased, 

NOX emissions decreased with increasing ethanol 

for vehicles that applied LTFT to power enrichment, 

while NOX emissions increased for vehicles that did 

not apply LTFT to power enrichment. 

7. Composite emissions trends for NMOG, NMHC, and 

CO were generally consistent with phase emissions 

results for all three phases. 

8. Composite emissions trends for ethanol, 

acetaldehyde, and formaldehyde were generally 

driven by phase 1 results. 

9. Composite emissions trends for NOX were strongly 

driven by phase 3 results. 

10. Catalyst temperatures during WOT operation were 

higher for vehicles that did not apply LTFT during 

power-enrichment operation. Vehicles found to apply 

LTFT during power enrichment showed no 

significant difference in catalyst temperature during 

WOT operation. 

ACKNOWLEDGMENTS 

This work was sponsored by the U.S. Department of 

Energy (DOE) Office of Energy Efficiency and 

Renewable Energy (EERE) Biomass Program and the 

EERE Vehicle Technologies Program. The authors 

gratefully acknowledge the support of Program 

Managers Joan Glickman and Kevin Stork at DOE. 

Contributions from staff at each of the testing labs—

CDPHE, TRC, and ORNL—are also greatly appreciated. 

The authors also acknowledge the contributions of 

Argonne National Laboratory for contracting assistance 

at TRC. This work has benefited greatly from 

consultation with many technical experts in industry and 

other government agencies. 

14
REFERENCES 

1. Energy Independence and Security Act of 2007, 

H.R. 6, 110th Congress, 2007-2008. 

2. R. Bechtold, J. F. Thomas, S. P. Huff, J. P. Szybist, T. J. 

Theiss, B. H. West, M. Goodman, T. A. Timbario, 

“Technical Issues Associated with the Use of Intermediate 

Ethanol Blends (>E10) in the U.S. Legacy Fleet,” ORNL/ 

TM-2007/37, August 2007. 

3. D. Guerrieri, P. Caffrey, V. Rao, “Investigation into the 

Vehicle Exhaust Emissions of High Percentage Ethanol 

Blends,” SAE Technical Paper 950777, 1995. 

4. Orbital Engine Company, “Market Barriers to the Uptake of 

Biofuels Study, A Testing Based Assessment to 

Determine Impacts of a 20% Ethanol Gasoline Fuel Blend 

on the Australian Passenger Vehicle Fleet,” Report to 

Environment Australia, March 2003. 

5. A. M. Hochhauser, “Review of Prior Studies of Fuel Effects 

on Vehicle Emissions,” CRC Report No. E-84, 

Coordinating Research Council, Alpharetta, GA, 2008. 

6. California Environmental Protection Agency, Air Resource 

Board, “California Non-Methane Organic Gas Test 

Procedure,” July 2002. 

7. K. Knoll, B. West, W. Clark, R. Graves, J. Orban, S. 

Przesmitzki, T. Theiss, “Effects of Intermediate Ethanol 

Blends on Legacy Vehicles and Small Non-Road Engines, 

Report 1 – Updated,” NREL/TP-540-43543 and 

ORNL/TM-2008/117, February 2009. 

8. W. O. Siegl, J. F. O. Richert, T. E. Jensen, D. Schuetzle, 

S. J. Swarin, J. F. Loo, A. Prostak, D. Nagy, A. M. 

Schlenker, “Improved Emissions Speciation Methodology 

for Phase II of the Auto/Oil Air Quality Improvement 

Research Program—Hydrocarbons and Oxygenates,” 

SAE Technical Paper 930142, 1993. 

9. J. F. Loo and D. T. Parker, “Evaluation of a Photoacoustic 

Gas Analyzer for Ethanol Vehicle Emissions 

Measurement,” SAE Technical Paper 2000-01-0794, 

2000. 

10. “Energy Policy Act (EPAct)/Testing Status,” Presentation 

by EPA to CRC Emissions Committee Meeting, RFS2 

Docket, EPA-HQ-OAR-2005-0161, Item EPA-HQ-OAR0161-0643, May 22, 2008. 

11. “Mid-Level Ethanol Blends Catalyst Durability Study 

Screening,” CRC Report No. E-87-1, Coordinating 

Research Council, Alpharetta, GA, 2009. 

12. California Environmental Protection Agency, Air 

Resources Board, “Driving Patterns and Emissions: A 

New Testing Cycle,” Research Notes No. 96-11, 1996. 

13. T. D. Durbin et al., “The Effect of Fuel Sulfur on NH3 and 

Other Emissions from 2000-2001 Model Year Vehicles,” 

CRC Report No. E-60, Coordinating Research Council, 

Alpharetta, GA, 2003. 

14. M. Skoglundh and E. Fridell, “Strategies for Enhancing 

Low-Temperature Activity,” Topics in Catalysis, Vol. 28, 

79-87, 2004. 

15. T. Kobayashi, S. Nagatomo, K. Ishikawa, T. Yamada, 

“Improvement of NOX Performance and Thermal Stability 

in Pd-Based Catalyst,” SAE Technical Paper 2000-01­

2927, 2000. 

16. J. Li, J. Theis, W. Chun, C. Goralski, R. Kudla, J. Ura, W. 

Watkins, M. Chattha, R. Hurley, “Sulfur Poisoning and 

Desulfation of the Lean NOX Trap,” SAE Technical Paper 

2001-01-2503, 2001. 

17. J. E. Thoss and J. Rieck, “The Impact of Fuel Sulfur Level 

on FTP Emissions – Effect of PGM Catalyst Type,” SAE 

Technical Paper 970737, 1997. 

18. C. H. Schleyer, R. F. Gunst, J. Eckstrom, J. Freel, R. A. 

Gorse, G. J. Barnes, K. D. Eng, M. Natarajan, A. M. 

Schlenker, “Effect of Fuel Sulfur on Emissions in California 

Low Emission Vehicles,” SAE Technical Paper 982726, 

1998. 

19. C. H. Schleyer, K. D. Eng, R. A. Gorse, R. F. Gunst, J. 

Eckstrom, J. Freel, M. Natarajan, A. M. Schlenker, 

“Reversibility of Sulfur Effects on Emissions of California 

Low Emission Vehicles,” SAE Technical Paper 1999-01­

1544, 1999. 

20. J. Yanowitz and R. L. McCormick, “Effect of E85 on 

Tailpipe Emissions from Light-Duty Vehicles,” Journal of 

Air & Waste Management, Vol. 59, 172-182, 2009. 

21. Code of Federal Regulations: Protection of the 

Environment, Title 40 CFR 86.1823-08. 

22. E. Nam, “Drive Cycle Development and Real-World Data 

in the United States,” Presentation at the United Nations 

Economic Commission for Europe, WLTP-02-17, January 

2009. 

23. H. C. Watson, E. E. Milkins, M. O. Preston, C. 

Chittleborough, B. Alimoradian, “Predicting Fuel 

Consumption and Emissions – Transferring Chassis 

Dynamometer Results to Real Driving Conditions,” SAE 

Technical Paper 830435, 1983. 

24. H. C. Watson, “Effects of a Wide Range of Drive Cycles 

on the Emissions from Vehicles of Three Levels of 

Technology,” SAE Technical Paper 950221, 1995. 

DISCLAIMER 

This manuscript has been authored by a contractor of 

the U.S. government under contract numbers NREL/DEAC36-08-GO28308 and ORNL/DE-AC05-00OR22725. 

Accordingly, the U.S. government retains a 

nonexclusive, royalty-free license to publish or 

reproduce the published form of this contribution, or 

allow others to do so for the U.S. government. 

15
 

DEFINITIONS, ACRONYMS, ABBREVIATIONS 

ANL Argonne National Laboratory 

ASTM American Society for Testing and 

Materials 

CDPHE Colorado Department of Public 

Health and Environment 

CFR Code of Federal Regulations 

CO carbon monoxide 

CRC Coordinating Research Council 

DOE U.S. Department of Energy 

DNPH dinitrophenylhydrazine 

DVPE dry vapor pressure equivalent 

ECU engine control unit 

EERE Office of Energy Efficiency and 

Renewable Energy 

EISA Energy Independence and Security 

Act 

EGO exhaust gas oxygen (sensor) 

EPA Environmental Protection Agency 

EPAct Energy Policy Act 

FFV flexible-fuel vehicle 

FID flame ionization detector 

FTP Federal Test Procedure 

GM General Motors 

LEV low-emission vehicle 

LHV 

LTFT 

MIL

NLEV 

NMHC 

NMOG 

NOX 

NREL 

OBD 

OEM 

ORNL 

RFS 

SG 

SRC 

STFT 

THC 

TRC 

UEGO 

ULEV 

VW 

WOT

lower heating value 

long-term fuel trim 

 malfunction indicator light 

National Low Emissions Vehicle 

nonmethane hydrocarbons 

nonmethane organic gas 

oxides of nitrogen 

National Renewable Energy 

Laboratory 

on-board diagnostics 

original equipment manufacturer 

Oak Ridge National Laboratory 

Renewable Fuel Standard 

specific gravity 

standard road cycle 

short-term fuel trim 

total hydrocarbon 

Transportation Research Center 

universal exhaust gas oxygen 

ultra-low emission vehicle 

Volkswagen 

 wide-open throttle 

16