NREL is a national laboratory of the U.S. Department of Energy, Office of Energy 

Efficiency & Renewable Energy, operated by the Alliance for Sustainable Energy, LLC.

Contract No. DE-AC36-08GO28308

The Impacts of Mid-Level Biofuel 

Content in Gasoline on SIDI 

Engine-Out and Tailpipe 

Particulate Matter Emissions 

Preprint

Xin He, John C. Ireland, Bradley T. Zigler, 

Matthew A. Ratcliff, Keith E. Knoll and

Teresa L. Alleman

National Renewable Energy Laboratory

John T. Tester

Northern Arizona University

Presented at the SAE 2010 Powertrains, Fuels and Lubricants 

Meeting

San Diego, California

October 25–27, 2010

Conference Paper

NREL/CP-5400-49311

February 2011
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1 

The Impacts of Mid-Level Biofuel Content in Gasoline on SIDI 

Engine-Out and Tailpipe Particulate Matter Emissions 

Xin He, John C. Ireland, Bradley T. Zigler, Matthew A. Ratcliff, Keith E. Knoll,

and Teresa L. Alleman

National Renewable Energy Laboratory 

John T. Tester

Northern Arizona University

ABSTRACT

In this work, the influences of ethanol and iso-butanol blended with gasoline on engine-out and post three-way 

catalyst (TWC) particle size distribution and number concentration were studied using a General Motors (GM) 

2.0L turbocharged spark ignition direct injection (SIDI) engine. The engine was operated using the production 

engine control unit (ECU) with a dynamometer controlling the engine speed and the accelerator pedal position 

controlling the engine load. A TSI Fast Mobility Particle Sizer (FMPS) spectrometer was used to measure the 

particle size distribution in the range from 5.6 to 560 nm with a sampling rate of 1 Hz. U.S. federal certification 

gasoline (E0), two ethanol-blended fuels (E10 and E20), and 11.7% iso-butanol blended fuel (BU12) were 

tested. Measurements were conducted at 10 selected steady-state engine operation conditions. 

Bi-modal particle size distributions were observed for all operating conditions with peak values at particle sizes 

of 10 nm and 70 nm. Idle and low-speed / low-load conditions emitted higher total particle numbers than other 

operating conditions. At idle, the engine-out particulate matter (PM) emissions were dominated by nucleation 

mode particles, and the production TWC reduced these nucleation mode particles by more than 50%, while 

leaving the accumulation mode particle distribution unchanged. At an engine load higher than 6 bar net mean 

effective pressure (NMEP), accumulation mode particles dominated the engine-out particle emissions, and the 

TWC had little effect. Compared to the baseline gasoline (E0), E10 does not significantly change PM

emissions, while E20 and BU12 both reduce PM emissions under the conditions studied. Iso-butanol was 

observed to impact PM emissions more than ethanol, with up to 50% reductions at some conditions. 

In this paper, issues related to PM measurement using the FMPS are also discussed. While some uncertainties 

are due to engine variation, the FMPS must be carefully maintained in order to achieve repeatable measurement

results.

INTRODUCTION

Increasing the production and use of biofuels is one of the major approaches to reducing the nation's 

dependence on foreign oil. Biofuels can also achieve significant reductions in greenhouse gases compared to 

fossil fuels [1]. In 2010, the U.S. Environmental Protection Agency (EPA) published the Renewable Fuel 

Standard Program Final Rule. The new renewable fuel standards increase the total volume of renewable fuel 

required to be blended into transportation fuel to 36 billion gallons by 2022 [2]. Over the next several years, 

ethanol and biodiesel are expected to make up the majority of this requirement. Numerous studies have been 

conducted to evaluate the impacts of mid-level ethanol blends (ethanol blends up to 20 vol %) on vehicles and 
2 

engines. 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, two national laboratories—the 

National Renewable Energy Laboratory (NREL) and the Oak Ridge National Laboratory—collaborated with 

industry and other experts to design and execute a test program that assesses the potential impacts of 

intermediate ethanol blends on typical vehicles as well as other engines using gasoline [3, 4]. The test program 

focuses specifically on the effects of E15 and E20 on regulated tailpipe emissions, engine durability, drivability, 

and materials compatibility. In a separate effort, Environment Canada also studied the effects of intermediate 

ethanol blends on vehicle tailpipe emissions [5-7] and evaporative emissions [8]. 

Over the past 10 years, there has been increasing evidence that particles generated by the combustion of fossil 

fuels adversely affect health [9]. Nano-scale particles are of particular concern because they are reported to be 

small enough to penetrate cell membranes and defenses, yet they are large enough to interfere with normal cell 

processes, damage DNA, and increase cancer risk [10]. In Europe, a particle number (PN) emission limit of 

6 × 1011 km-1 (Particle Measurement Programme method, New European Driving Cycle test) becomes effective 

at the Euro 5/6 stage for all categories of diesel vehicles. A PN emission limit for gasoline vehicles is to be 

defined by September 2014 [11]. The establishment of these limits has led to numerous studies of particle size 

distribution. With the application of the diesel particle filter (DPF), tailpipe particle emissions from diesel 

engines have been greatly reduced. Recent studies comparing gasoline direct injection engines and diesel 

engines showed higher PN emissions from gasoline direct injection engines relative to diesel engines equipped 

with DPFs [12, 13]. 

Fuel properties have significant impacts on PM emissions. Researchers have found significant reduction in 

engine-out PM mass emissions from diesel engines by using biodiesels [14]. Price et al. [15] found higher PM

emissions using toluene compared to iso-octane. However, the impacts of biofuels (such as ethanol) on gasoline 

engine PN counts are rather controversial [16, 17]. Ericsson et al. [13] studied the tailpipe particulate emissions 

from port and direct-injected vehicles with E5 and E85 fuels. They found lower PNs and total mass by using 

biofuels. Czerwinski et al. [18] studied nano-particle emissions from two-stroke scooters with ethanol blends. 

The results show little effects of nano-particle emissions when ethanol was added. Muralidharan et al. [19] 

studied the characterization of particulates with different blends of ethanol-gasoline in scooters. The average PN

concentration did not show any particular trend as the percentage of ethanol in gasoline was increased from 5 to 

30 percent. More studies are needed to reveal the impacts of biofuels on PN emissions from gasoline engines.

Although some devices have been developed to measurement PN concentration and size distribution, it has 

never been easy to get reliable and repeatable results. Previous studies have reported high measurement 

uncertainty and poor experimental repeatability. Hall and Dickens [20] found that PNs from vehicles and 

sampling systems are strongly dependent on their pre-history. Mohr et al. [21] found that the sampling method 

has a high influence on the results of the total number and number size distribution. Li et al. [22] measured the 

PN using a condensation particle counter and reported poor repeatability of the results. Zervas et al. [23] 

compared diesel and gasoline particle size distribution using a Scanning Mobility Particle Sizer and an electrical 

low pressure impactor. They found particle measurements from gasoline engines have a high standard 

deviation. 

Recently, a GM Ecotec "LNF" family 2.0L SIDI turbocharged gasoline engine was installed and instrumented 

in the Renewable Fuels and Lubricants (ReFUEL) research laboratory at NREL, which provides an opportunity 

for detailed investigation on the effects of biofuels on engine performance and emissions. As part of larger 

effort to establish baseline performance of the production engine and control system before conversion to 

single-cylinder operation [24], this study focused on particulate emissions, both pre- and post-TWC at steadystate conditions. 
3 

EXPERIMENTAL SETUP

ENGINE

The engine used in this study was a production 2009 GM Ecotec "LNF" 2.0L turbocharged engine, which uses a 

wall-guided SIDI combustion system. Table 1 lists the engine specifications. Figure 1 shows the schematic of 

the engine combustion system, including the combustion chamber, piston, valves, spark plug, and fuel injector. 

In a wall-guided SIDI engine, fuel is injected into the combustion chamber from a side-mounted injector. The 

fuel–air mixture is then guided towards the spark plug by a special piston recess, assisted by a reverse tumble. 

Fuel injection typically occurs during the intake stroke to ensure sufficient fuel air mixing before combustion 

starts. Under most engine operating conditions, the engine burns near stoichiometric conditions so that a TWC

can be used to reduce emissions of pollutants. One of the major disadvantages of the wall-guided SIDI engine is 

high particulate emissions [12, 13]. 

The study used the production ECU, which utilized the original equipment manufacturer's (OEM's) calibration 

for the engine and emission control system from a 2009 Chevrolet HHR-SS (a non–flex-fuel vehicle). The 

engine was connected to a 75-HP AC dynamometer. Although limitations of the engine dynamometer prevented

running the engine at its full rated power, it was adequate to cover a majority of federal test procedures and 

US06 engine operating conditions. 

The engine was fully instrumented. Cylinder pressure was measured by replacing one production spark plug 

with a Kistler measuring spark plug with an integral 3-mm cylinder pressure sensor (type 6118BCD25A41). 

Intake manifold pressure, exhaust manifold pressure, and fuel rail pressure were measured using Kistler 

pressure transducer types 4005BA5FA2, 4007BA5FA2, and 4065A500A2, respectively. Tektronix current 

probes (Model A622) were used to measure the spark and fuel injection signals sent from the ECU. Signals 

from both intake and exhaust camshaft position sensors were also recorded. An AVL IndiMODUL data 

acquisition system was used to collect high-speed data with resolution of 0.2 crank angle degrees (CAD). 

K-type thermocouples were used to monitor ambient air temperature, air temperature after compressor, intake 

manifold air temperature, exhaust gas temperature, gas temperature after turbine, engine coolant temperature, 

and engine oil temperature. The low-speed data were collected using a Sakor data acquisition system at a 

sampling rate of 1 Hz. Exhaust emissions were measured using a Sensors SEMTECH portable emissions 

measurement system (PEMS) capable of recording total hydrocarbons (THC), carbon monoxide (CO), carbon 

dioxide (CO2), and oxides of nitrogen (NOx).

Table 1. Engine Specifications 

Displacement 1,998 [cc]

Number of cylinders 4

Bore 86.0 [mm]

Stroke 86.0 [mm]

Connecting Rod Length 145.5 [mm]

Compression Ratio 9.2
4 

Figure 1. Schematic of the Engine Combustion System 

TSI FAST MOBILITY PARTICLE SIZER (FMPS)

The PN size distribution was measured using a TSI FMPS spectrometer (Model 3091). The FMPS spectrometer 

performs particle size classification based on differential electrical mobility classification. The charged aerosol 

enters the analyzer column near on-axis and above the central rod. The particles are deflected radially outward 

and collected on electrically isolated electrodes that are located at the outer wall. The PN concentration is 

determined by measuring the electrical current collected on electrodes. An inversion algorithm is used to 

deconvolute the data and make corrections for the image charges and the time delays in the column, converting 

currents from the electrometers into 32channels of output. This process allows the maximum resolution of the 

instrument to be represented by output channels that are equally spaced on a log scale between 5.6 nm and 560 

nm [25]. In this study, the data were collected at a sampling rate of 1 Hz for 3 minutes. The results presented are 

the averaged PN with the error bar representing the standard deviation. 

PN measurement is very sensitive to the sample's relative humidity [26], especially when measuring nucleation 

mode particles. In order to prevent water condensation and to minimize semi-volatile nucleation in the sampling 

system, the exhaust samples were diluted using a two-stage dilution system, achieving a total dilution ratio of 

about 10:1. Figure 2 shows the schematic of the exhaust sampling system. The sample lines in red are heated to 

190°C. Engine-out samples were extracted 30 cm downstream of the engine turbine. The post-TWC emissions 

were extracted 10 cm downstream of the engine TWC. The dilution gas was generated by a Parker Balston 

purge gas generator (Model 75-45-12VDC), which provided clean, dry, and CO2-free air. Two mass flow 

controllers (MFC) control the dilution gas flow rate. The first stage dilution ratio was about 5:1, and the dilution 

gas was heated above 100°C by the heated sample line to minimize semi-volatile nucleation. The second stage 

dilution gas was at ambient temperature to cool the sample gas. Stainless steel tubing was used after the second 

stage dilution, which further cooled the sample gas to about 45°C before entering the FMPS. The estimated 

residence time in the sample line is about 3 seconds. During the experiment, only one of the solenoid valves 

was opened at a time. When solenoid valve 1 was opened, PEMS measured the raw engine exhaust. When 

solenoid valve 2 was opened, PEMS measured the diluted exhaust sample after the FMPS. Since the dilution 

gas is a CO2-free air, the dilution ratio can be calculated based on the pre- and post-FMPS CO2 concentration 

using Equation (1): 
5 

 ൌ ߙ

ቂ஼ைమ೏ೝ೤ቃ

೐೙೒೔೙೐ ೚ೠ೟ ቀଵ଴଴ା ቂ஼ைమ೏ೝ೤ቃ ೐೙೒೔೙೐ ೚ೠ೟ൈቀಹ

಴ ൗ ቁ/ଶቁ

ቂ஼ைమ೏ೝ೤ቃ

ೌ೑೟೐ೝ ೏೔೗ೠ೟೔೚೙ ቀଵ଴଴ା ቂ஼ைమ೏ೝ೤ቃ ೌ೑೟೐ೝ ೏೔೗ೠ೟೔೚೙ൈቀಹ

಴ ൗ ቁ/ଶቁ (1) 

in which (H/C) is the fuel hydrogen to carbon ratio. 

Figure 2. Schematic of Exhaust Sampling System 

FUELS 

Ethanol-blended fuels (previously used for a mid-level ethanol blend study at NREL [3, 4]) were used in this 

study. Three fuels of varying ethanol or iso-butanol blend levels were included in this study to determine the 

effects of alcohol content and type on exhaust emissions. Certification gasoline (E0) was included in this study 

for a baseline comparison. Ethanol or iso-butanol blend concentration levels were specified on a volumepercent basis. Fuel-grade ethanol (per ASTM D 4806) supplied by Gage Products Company was used in this 

study. Iso-butanol was purchased from Industrial Chemicals Corporation. Table 2 summarizes the selected fuel 

properties. Fuels were splash blends of E0 (certification gasoline, i.e., Indolene). Ethanol-blended fuels were 

analyzed by the Fuel Analysis Laboratory at the Southwest Research Institute. An 11.7 vol % iso-butanol blend 

(listed as "BU12" in Table 2) represents the highest oxygen content in gasoline (2.7%) currently allowed by the 

EPA. The properties of BU12 were calculated based on the properties of the measured E0 and pure iso-butanol. 

Table 2. Test Fuel Properties 

Fuel 

%-EtOH/IBOH 

 (vol-%) 

LHV 

(MJ/kg) RON MON (R+M)/2 SG 

C

(wt%) 

H

(wt%) 

O

(wt%) 

H:C O:C 

T90 

(°C) 

E0 0 43.03 97.1 88.3 92.7 0.745 86.03 13.18 0 1.826 0 159.1

E10 9.83 41.12 100 89.7 94.85 0.749 82.69 13.16 3.62 1.896 0.0329 156.2

E20 19.43 39.52 101.2 90.2 95.7 0.7532 79.5 13.11 7.112 1.965 0.0672 151.2

BU12 11.70 41.77 NA NA NA NA 83.38 13.23 2.7 1.891 0.0243 NA
6 

ENGINE OPERATION CONDITIONS

Experiments were conducted at 10 steady-state engine operating conditions, which are listed as engine speed 

and NMEP in Table 3. The value "800 rpm - 1 bar" represents the engine running at idle. In this paper, "speedNMEP" will be used to represent an engine operation condition. For example, "1000-3" means the engine was 

running at 1,000 rpm and 3 bar NMEP. While steady engine oil and coolant temperature (about 88°C) were 

controlled by engine ECU at most operating conditions, slow increases in engine oil and coolant temperature 

were observed at "3000-6" and "3000-9" due to the limited cooling capability of the engine radiator in the test 

cell. 

Table 3. Engine Operation Conditions 

Engine Speed (rpm) Engine NMEP (bar)

800 1

1000 3

1500 3 and 6

2000 3, 6, and 9

3000 3, 6, and 9

RESULTS AND DISCUSSION

TOTAL PN CONCENTRATION

It is now generally accepted that automotive particle emissions fall into two broad categories: accumulation 

mode particles and nucleation mode particles [27]. Accumulation mode particles are mainly carbonaceous in 

nature and greater than 30 nm in particle size [27]. Nucleation mode particles, with particle sizes generally 

below 30 nm, comprise predominantly condensed volatile material, mainly sulfate and heavy hydrocarbons 

[27]. Nucleation mode particles are formed during combustion and dilution, usually through homogenous and 

heterogeneous nucleation mechanisms [28]. Nucleation mode particles are more sensitive to temperature, 

humidity, dilution, and sampling system factors [26]. For the initial discussion, the FMPS particle size data are 

collapsed into total particle counts for these two particle size regions. Data presented in this section are preTWC emissions. 

Figure 3(a) shows the total nucleation mode PN concentration at the conditions studied; Figure 3(b) shows a 

rescaled subset of conditions where "800-1" and "1000-3" have been removed so that the remaining operational 

modes are better defined. Figure 4(a) shows the total accumulation mode PN concentration at the conditions 

studied; Figure 4(b) shows a rescaled subset of conditions for greater clarity. It is quite obvious that at low 

engine speeds (<1,500 rpm), the total nucleation PN concentration is more than 3 times higher than other 

conditions. A comparison of "800-1" and "1000-3" reveals that nucleation mode PN and size distribution do not 

change significantly. The major difference is related to the accumulation mode particles. At 2,000 rpm, the 

nucleation mode PN distributions are almost the same when load is increased from 3 to 6 bar. Again, the major 

difference is related to the accumulation mode particles. As the load was further increased to 9 bar, both 

nucleation mode and accumulation mode particles increased. In summary, a clear trend of an increase in the 

total accumulation mode PN concentration with engine speed and load was observed at engine speeds higher 

than 1,500 rpm. 

Upon examining the engine calibration, it was discovered that the engine control strategy at low speed and low 

load is different from other conditions. At "800-1" and "1000-3," fuel rail pressure is low and very unstable. 
7 

This may be partially due to the OEM's use of a three-lobe, cam-driven high-pressure fuel pump feeding a 

common fuel rail for all four cylinders. Fuel pressure oscillation differences across each fuel injector feed likely 

presented a significant design and control challenge. Another major difference at low engine speeds is the fuel 

injection timing, which is presented in Figure 5. The black solid line represents the boundary of the two fuel 

injection control strategy regions. At low speed and low load (lower left corner in Figure 5), fuel injection 

timing is retarded as engine speed and load increase. In the other regions, fuel injection is advanced with 

increasing engine speed and load. Fuel injection timing is one of the dominant factors influencing PN

emissions. Figure 6 shows the nucleation mode and accumulation mode PN concentration as a function of fuel 

injection timing at eight operating conditions studied (excluding "800-1" and "1000-3"). Disregarding the 

results at idle, a clear trend of increasing total accumulation PN emissions with advancing fuel injection timing

was observed. Nucleation mode PN emissions also increased with advancing fuel injection timing. The increase 

in PN emissions is most likely due to the increasing liquid fuel impingement on the piston bowl. This may result 

in liquid fuel that is not totally vaporized and well mixed with the ambient air at the start of combustion. As a 

consequence, local fuel-rich combustion or even pool fire could occur near the piston, generating high 

emissions of PM. It is worth noting that although good correlation was observed between PN emissions with 

fuel injection timing, other parameters, such as fuel injection pressure, could also influence PN emissions. The 

best way to reveal the influence of fuel injection timing on PN emissions is to conduct a fuel injection sweep 

study while maintaining other parameters constant. This will be included in a future study with independent 

engine control. 

Figure 3 and Figure 4 also reveal the effects of biofuels on total PN emissions. Generally speaking, biofuels 

reduce both nucleation and accumulation PN emissions. At idle, "1000-3", and "3000-6", E10 generates higher 

nucleation mode particles. At most of the remaining conditions, increasing biofuel content reduces nucleation 

mode particles. At 6 bar NMEP, E10 generates about 15% higher accumulation mode particles than E0. For all 

other conditions, increasing biofuel content reduces accumulation mode particles. As will be discussed in the 

next section, this observation for E10 loses its strength when examining the detailed PN distribution data. Isobutanol exhibited stronger effects in reducing both nucleation mode and accumulation mode PN emissions. 

 (a) (b) 

Figure 3. Nucleation Mode PN Concentration 
8 

 

(a) (b) 

Figure 4. Accumulation Mode PN Concentration 

Figure 5. Fuel Injection Timing (–360 CAD is the Beginning of the Intake Stroke; 0 CAD is the Compression 

TDC.) 
9 

 

(a) (b) 

Figure 6. The Influence of Fuel Injection Timing on Nucleation Mode and Accumulation Mode PN 

Concentration 

PN DISTRIBUTION

In this section, only pre-TWC particle size distribution at "800-1", "1000-3", "2000-3", "2000-6", and "2000-9" 

conditions are presented. At speeds higher than 1,500 rpm, although the total PN concentration increases with 

increasing engine speed, the particle size distribution does not change significantly. It is worth noting that 

engine calibration parameters such as intake manifold pressure, fuel injection timing, cam phaser position, and 

spark timing do not change significantly with engine speed, but are strong functions of engine load. Thus, three 

load points at 2,000 rpm were selected for discussion here. 

Particle size distributions and the effects of biofuel in reducing PN at selected conditions are presented in 

Figures 7 through 11. The x-axis displays the mid-point particle diameters, equally spaced on a log scale 

between 5.6 nm and 560 nm. The PN concentration is normalized to the bin width and displayed on the y-axis 

as dN/dlogDp (#/cc). In this case, the normalized PN concentration is calculated by multiplying the PN 

concentration by 16, the number of channels per decade. A bi-modal particle size distribution was observed at 

all conditions with peaks at 10 nm and 70 nm. We also observed a small peak at 20 nm. However, this small 

peak may not actually be due to the higher particle concentration in this size range. It may instead be an artifact 

of the way the FMPS groups the particle sizes, electrometer noise, or a poor FMPS deconvolution algorithm. 

The following discussion focuses on the most prominent peaks (10 nm and 70 nm). 

Figure 7(a) shows the particle size distribution at "800-1". At this operating condition, nucleation mode 

particles dominate the total particle emissions. However, due to the small size of nucleation mode particles, the 

mass percentage counts for less than 25% of total mass emitted. The effect of ethanol on PN emission is quite 

complicated. It is worth noting that the coefficient of variation of engine NMEP is about 10% at this engine 

operating condition, which is the primary reason for the high measurement uncertainty (the sample standard 

deviation is represented by the error bars), especially for nucleation mode particles. On average, while E10 

generates more nucleation mode particles than E0, the opposite was observed for E20. Although up to 40% 

differences in PN emission were observed, the uncertainty of the different samples envelop the sample means. 

BU12 had the lowest PN concentration at all size ranges. On average, BU12 reduced nucleation mode and 

accumulation mode particles by 50% and 30%, respectively. 
10 

 

(a) (b) 

Figure 7. Particle Size Distribution and the Effects of Biofuels on PN Reduction at 800 rpm–1 bar NMEP 

 

(a) (b) 

 Figure 8. Particle Size Distribution and the Effect of Biofuels on PN Reduction at 1,000 rpm–3 bar NMEP 
11 

(a) (b) 

Figure 9. Particle Size Distribution and the Effect of Biofuels on PN Reduction at 2,000 rpm–3 bar NMEP 

(a) (b) 

Figure 10. Particle Size Distribution and the Effect of Biofuels on PN Reduction at 2,000 rpm–6 bar NMEP 
12 

(a) (b) 

Figure 11. Particle Size Distribution and the Effect of Biofuels on PN Reduction at 2,000 rpm–9 bar NMEP 

At "1000-3" and engine load higher than 6 bar NMEP, accumulation mode particulates dominate the total PN 

emissions. The peaks are all observed at about 70 nm. Compared to E0, E10 has very similar total PN and PN 

size distribution. At most conditions, the differences are within 20%. The only exception is higher accumulation 

mode particle emissions at "2000-6". Figure 8 shows the particle size distribution and effect of biofuels on PN 

reduction at "1000-3". Both E20 and BU12 show significant PN reduction at most size ranges. A higher 

percentage reduction is observed for large size particles. The particle size distribution and effect of biofuels on 

PN percentage reduction at "2000-3", "2000-6", and "2000-9" are presented in Figures 9 through 11. At these 

three conditions, both E20 and BU12 show a relatively constant percentage reduction of the nucleation mode 

particles. E20 reduced nucleation mode PN by about 20%. BU12 reduced nucleation mode PN by about 30%. 

For accumulation mode particles, PN percentage reduction increased with particle size. BU12 had the lowest 

particle emissions at all size ranges. The particle size distributions at "1500-6" and "3000-6", while not 

presented in this paper, exhibited very similar trends to "2000-6". E10 did not exhibit the same behavior. In 

general, PN from E10 tracked closely with E0, except at 6 bar NMEP where E10 increased accumulation mode 

PN.

THE EFFECTS OF TWC ON PARTICLE EMISSIONS

In this study, the TWC was warmed up before measuring the PN by running the engine for 20 minutes at 1,000 

rpm at 6 bar NMEP. The measured total hydrocarbons (THCs) and nitrogen oxide (NOx) emissions after the 

TWC were very low at all conditions. Figure 12(a) compares the pre- and post-TWC PN distributions of E0 at 

idle; the dashed blue lines represent the PN reduction percentage with respect to the particle sizes. The TWC 

reduced the nucleation mode particles. Up to 50% increases in accumulation mode particles were observed after 

the catalyst. This could be due to the release of particles that were trapped in the TWC from prior experiments. 

It should be noted that the apparent increases of accumulation node particles are all within the measurement

uncertainty limits. Figure 12(b) compares the pre- and post-TWC PN distributions of E0 at "2000-6." Again, a 

reduction of nucleation mode particles was observed, but not as significant as at idle. Similar to idle, the 

percentage in reduction decreases with increasing particle size. Almost no difference was observed for particles 

larger than 30 nm. Figure 12(c) compares the pre- and post-TWC PN distributions of E0 at "3000-6". The 
13 

results are very similar to the "2000-6" condition. Clearly, nucleation mode particles are reduced. Although an 

up to 20% change in PN is also observed for accumulation mode particles, most are within the measurement 

uncertainty limits. 

Clearly, the TWC reduces nucleation mode particles. A higher percentage in PN reduction was observed for 

small particles. This could be due to the following two reasons. First, nucleation mode particles could vaporize 

and be oxidized by the TWC. At idle, the gas space velocity is very low, which gives more residence time for 

the particles in the TWC to be oxidized. This would explain the significant nucleation mode particle reduction 

at idle. Second, some particle nucleation may actually occur in the sampling line. As the TWC reduces 

hydrocarbon and volatile organic compounds, the effect may virtually eliminate any particle nucleation that 

might be occurring in the sampling line.

 

 (a) 800 rpm–1 bar, E0 (b) 2,000 rpm–6 bar, E0 

(c) 3,000 rpm–6 bar, E0 

Figure 12. The Effect of TWC on PN Emissions 
14 

UNCERTAINTIES IN PN MEASUREMENT

Similar to the PN measurement issues reported by other researchers [20–23], measurement repeatability was a 

primary concern during this study. In this study, the test cell temperature and humidity were not controlled due 

to the facility limitations. Engine coolant and oil temperature were controlled by the engine itself. No extra 

cooling capability was supplied. The engine radiator was able to maintain constant coolant and oil temperature 

at engine speeds up to 2,000 rpm. At "3000-6" and "3000-9" conditions, continuous increases in both coolant 

and oil temperatures were observed, which change the combustion chamber heat transfer rate. Higher 

combustion temperatures could increase soot formation. At these different environmental conditions, the ECU

could also use a different calibration table to control fuel injection timing and/or spark timing, which also could 

change PN formation. Figure 13 shows the time histories of the total PN concentrations and engine coolant and 

oil temperatures during the FMPS sampling period at "3000-6." PN concentrations increase with engine oil and 

coolant temperatures. It should be noted that the same data acquisition procedure was followed when testing 

different fuels at "3000-6" and "3000-9" conditions. For example, FMPS sampling started when the engine 

coolant reached 92°C. Although the "3000-6" and "3000-9" PN data presented in Figure 3 and Figure 4 were 

not truly taken at steady-state condition, they provide valuable comparison among different fuels. 

 Figure 13. The Effects of Engine Oil and Coolant Temperature on PN Emissions 

It is also very crucial to maintain constant engine loads to achieve good measurement repeatability. In this 

study, the engine load was controlled by the acceleration pedal position. This works very well at most of the 

selected conditions, except "1000-3". Figure 14 shows the effects of engine load swing on PN emissions at 

"1000-3". At this condition, although the acceleration pedal position was held constant, the engine load could 

swing between 2.8 and 3.1 bar. Total PN emissions changed with engine load. About 4 seconds lag of the 

measured PN concentration to the engine NMEP is due to the measurement delay of the sampling and 

measurement system. At "1000-3", a 10% change in engine load causes more than a 50% change in total PN 

emissions. It is worth noting that the data reported in Figure 8 were post-processed by selecting data at 2.8 bar 

NMEP. 

The FMPS is the other major source causing poor measurement repeatability. The first problem is due to 

potential FMPS baseline shifting during the continuous measurement of moderately high PN densities. Figure 

15 shows an example of poor measurement results due to an FMPS baseline shift. The engine was running at 

2,000 rpm and 9 bar NMEP. The solid red line represents the measured PN distribution. Right after the emission 

data were saved, the FMPS baseline data were taken by sending the purge gas into the FMPS, which is 
15 

indicated by the black dashed line. An FMPS baseline shift was observed at particle sizes less than 12.4 nm and 

most prominent at sizes between 70 nm and 255 nm. The blue dashed line shows the post-processed FMPS data 

by subtracting the baseline PN distribution. However, it does not always achieve consistent measurement 

results, which means the baseline could change continuously during the measurement. One method to 

compensate for this problem is to purge the FMPS with clean gas and reset (or re-zero) the background. A long 

purge time, usually several hours, may be required to eliminate the baseline shift. It should be noted that 

purging the FMPS may not always remove the baseline shift. In this circumstance, the best solution for 

removing the baseline shift is to clean the FMPS. As part of this study, the FMPS baseline was checked prior to 

the start of each data sampling event. 

The second problem is due to observed changes in the FMPS sensitivity over time. The authors are not certain 

of the root cause of this problem, but speculate that it could be due to the non-constant charge of the FMPS 

charge needle after it is covered with visible soot, or it could be some inherent change in the FMPS electrometer 

sensitivity over time. Figure 16 compares the measurement results when (for two cases) the FMPS had been 

used for more than 8 hours to continuously measure moderately high PN concentration values (i.e., a "dirty" 

FMPS) and (for two cases) after the FMPS was cleaned following the process specified by the FMPS user 

manual (a "clean" FMPS). A clean FMPS always measured higher PN concentrations than a dirty FMPS. It was 

also observed that a clean FMPS achieves much better measurement repeatability, as shown in Figure 16. 

Although the FMPS user manual [25] recommends cleaning the charge needle every 100 hours and cleaning 

electrometers every 500 hours, the authors established a procedure to clean and zero the FMPS about every 8 

hours to achieve good repeatability for the sample exhaust conditions measured for this study. 

Figure 14. The Effects of Engine Load Swing on PN Emissions 
16 

Figure 15. The Effects of FMPS Background Shift on PN Measurements 

Figure 16. A Comparison of the Measurement Results Between a "Dirty" FMPS and a "Clean" FMPS

SUMMARY/CONCLUSIONS 

The impacts of mid-level biofuel content in gasoline engine PN emissions were studied using a GM 2.0L SIDI 

turbocharged engine. The particle size distribution both pre- and post-TWC was measured using a TSI FMPS

spectrometer. Although this study focused on studying the impacts of biofuel content and type, the results also 

partially unveil the effects of some key engine operating parameters on PN emissions, which is very valuable 

for auto manufacturers in designing better SIDI engines with lower pollutant emissions. 

The major conclusions from this study are:

(1) E10 exhibited almost the same particle emissions as E0. E20 and BU12 reduced particle emissions in all 

conditions studied. Under most operating conditions, BU12 achieved a 30% reduction in nucleation mode 

particles, while E20 achieved about a 20% reduction. E20 and BU12 achieved a higher percentage of 

accumulation mode PN reduction than reduction in nucleation mode particles. 
17 

(2) A bi-modal PN size distribution was observed at all operating conditions with peaks at 10 nm and 70 nm. At

idle, nucleation mode particles dominated the particle emissions. At a load higher than 6 bar NMEP, 

accumulation mode particles account for more than 60% of total PN emissions.

 (3) Fuel injection timing is one of the major factors that influence particle emissions. Accumulation mode 

particulate emission correlates well with fuel injection timing. For the wall-guided SIDI engine, fuel piston 

impingement could be one of the key reasons for high PN emissions. Advancing the fuel injection timing 

increases the possibility of liquid fuel impinging on the piston bowl, which could be the major reason for high 

PN emissions at low speed / low load conditions. 

(4) The TWC reduces PN emissions at idle, where the nucleation mode particulates dominate the total PN 

emissions. The TWC does not change accumulation mode PN emissions. 

(5) The PN emissions are sensitive to engine operating conditions. In this study, a change in total PN emissions 

with a change of oil and coolant temperature was observed. At some operating conditions, a 10% change in 

engine load could change total PN emissions by more than 50%. 

(6) The FMPS must be carefully maintained to achieve repeatable measurement results.

FUTURE WORK

The study utilized an interim development point of a research engine platform for fundamental fuel combustion 

studies. Future work will focus on developing this platform into a single-cylinder research engine. First, the 

production multi-cylinder engine will be converted to a single-cylinder engine with an independent engine 

control unit providing independent fuel injection, spark timing, fuel rail pressure, and cam phaser position 

control. As part of this conversion, a dedicated high-pressure fuel handling system will also eliminate unwanted 

fuel pressure oscillation effects inherent in the OEM system, which would otherwise become worse in a singlecylinder configuration. Second, the current dilution system could only provide reliably consistent data at a 

dilution ratio of about 10:1. This custom dilution system is designed to have a maximum dilution of around 

40:1. If higher particulate levels are expected in future research studies, a dilution system with a higher dilution 

ratio will be required. Third, it will be very important to develop a FMPS spectrometer calibration procedure for 

better measurement repeatability; it may be that each PM test scenario in the future must have a unique PN 

counter calibration procedure. Fourth, future work will also include the study of other un-regulated emissions.

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P-A., Carlsson, "Characterization of Particulate Emissions and Methodology for Oxidation of Particulates from 

Non-diesel Combustion Systems," SAE 2008-01-1746. 

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CONTACT INFORMATION

Xin He, National Renewable Energy Laboratory, 1617 Cole Blvd, MS 1634, Golden, CO 80401. 

Email: xin.he@nrel.gov 

ACKNOWLEDGMENTS

This work was sponsored by the U.S. DOE Vehicle Technologies Program. The authors gratefully acknowledge 

the support of DOE Fuels Technologies Program Manager Kevin Stork. The authors also greatly appreciate 

contributions from the ReFUEL research laboratory staff at NREL including Bob Moore, Scott Walters, Dan 

Pedersen, and Jonathan Burton. 

DEFINITIONS/ABBREVIATIONS 

CAD crank angle degree

CO carbon monoxide 

CO2 carbon dioxide 
20 

DOE Department of Energy 

DPF diesel particle filter

ECU engine control unit 

EERE Energy Efficiency and Renewable Energy

EPA Environmental Protection Agency

FMPS Fast Mobility Particle Sizer

GM General Motors

LHV lower heating value 

MFC mass flow controller

MON motor octane number 

NMEP net mean effective pressure

NOx nitrogen oxide 

NREL National Renewable Energy Laboratory 

OEM original equipment manufacturer

PEMS portable emissions measurement system

PM particulate matter

PN particle number 

ReFUEL Renewable Fuels and Lubricants Research Laboratory

RON research octane number

SG specific gravity

SIDI spark ignition direct injection

THC total hydrocarbons 

TWC three-way catalyst
F1147-E(10/2008) 

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4. TITLE AND SUBTITLE

The Impacts of Mid-Level Biofuel Content in Gasoline on SIDI 

Engine-Out and Tailpipe Particulate Matter Emissions: Preprint

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DE-AC36-08GO28308

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X. He, J.C. Ireland, B.T. Zigler, M.A. Ratcliff, K.E. Knoll, T.L.

Alleman, and J.T. Tester

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14. ABSTRACT (Maximum 200 Words)

The influences of ethanol and iso-butanol blended with gasoline on engine-out and post three-way catalyst (TWC) 

particle size distribution and number concentration were studied using a turbocharged spark-ignition direct-injection 

engine. Particle size distribution in the range of 5.6 to 560 nm was measured. U.S. federal certification gasoline (E0), 

two ethanol-blended fuels (E10 and E20), and 11.7% iso-butanol blended fuel (BU12) were tested at 10 selected 

steady-state engine operation conditions. Bi-modal particle size distributions were observed for all operating 

conditions with peak values at particle sizes of 10 nm and 70 nm. Idle and low-speed/low-load conditions emitted 

higher total particle numbers than other operating conditions. At idle, the engine-out particulate matter emissions 

were dominated by nucleation mode particles. The TWC reduced these nucleation mode particles by more than 50%; 

the accumulation mode particle distribution was unchanged. At an engine load higher than 6 bar net mean effective 

pressure, accumulation mode particles dominated the engine-out particle emissions, and the TWC had little effect. 

Compared to E0, E10 did not significantly change PM emissions, while E20 and BU12 reduced PM emissions. Isobutanol was observed to impact PM emissions more than ethanol, with up to 50% reductions at some conditions.

15. SUBJECT TERMS

gasoline; ethanol blended; biofuel; iso-butanol; particle size distribution; emissions

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