**MEMORANDUM**

**TO:** Docket EPA

- HQ

- OAR

- 2005

- 0161

**FROM** : Aron Butler, staff engineer, OAR/OTAQ/ASD

**SUBJEC T:**  Summary of recent findings for fuel effects of a 10% ethanol blend on light duty

exhaust emissions

**DATE:** J anuary 29 , 20 10

Background
Section 1506 of the Energy Policy Act of 2005 requires EPA to produce an updated fuel effects model representing the 2007 light

- duty gasoline fleet, including determination of the emissions impacts of increased renewable fuel use. Pursuant to this goal, o ur office , with support from the Department of Energy Office of Energy Efficiency and Renewable Energy , has undertaken a study to examine the effects of five fuel properties (ethanol, aromatics, vapor pressure, and two distill ation parameters : T50 and T90) on exhaust emissions from light

- duty vehicles meeting the latest federal emission regulations (known as the Tier 2 program). The initial phase was a pilot study of the effects of ethanol, done using a typical base conventiona l gasoline (0% ethanol, or E0) and a typical 10% ethanol blend (E10) between May 2008 and January 2009

. This memo specifically addresses effects of E10 relative to E0 on emissions of hydrocarbons (as NMHC) and nitrogen oxides (NOx) as suggested by th e pil ot study . Previous studies had suggested E10 blends produced different emission behavior for these pollutants in newer vs. older technology vehicles. 1 Data from this pilot study provides further such evidence, which we feel is sufficient to guide decisio ns related to inventory modeling

. 2 Other pollutants not covered by this memo (such as CO and air toxics) are being modeled assuming similar behavior for newer and older vehicles , consistent with recent data

. 1,2
The full fuel effects study, involving 31 fuels, is expected to be completed by mid

- 2010, and its results may supersede the findings described here. Emission behavior of other pollutants not covered here will be described in reports related to the full study, and in subsequent rulemaking actions that use those results.

Methods

The emissions testing used 19 vehicles covering a mix of passenger cars and light trucks , representing vehicles with high sales volumes . The test vehicle fleet is shown in Table 1. Two test fuels were produced containing 0% and 10% ethanol by volume , with other properties being

1 For more detailed discussion of emissions data sources, see Section 3 .1 of the RFS1 RIA, EPA

- 420

- R

- 07

- 004 , available at http://www.epa.gov/otaq/renewablefuels/420r07004chap3.pdf

. 2 For more det ailed discussion of inventory modeling for the final rulemaking, see Section 3.1 of the RFS2 RIA, EPA

- 420

- R

- 10

- 006, available at http://www.epa.gov/otaq/renewablefuels/

.similar to what would typically be found at commercial filling stations. These fuel properties are

given in Table 2.
The vehicles were tested at 75°F and 50°F using the LA92 test cycle, with each fuel being tested twice (two replicates) . Fuels were tested in ascending order of ethanol blend level. A speed versus time trace of the LA92 test cycle is shown in Figure 1. The three phases of the test cycle are designed to allow separation of start

- u p emissions (when the engine and catalyst are relatively cold) from fully

- warmed

- up driving (when operation of emission controls has stabilized). For purposes of estimating emission inventories , the phases are typically weighted together to form a single, composite emission factor (in grams per mile) to represent average driving patterns.

Results
The resulting emissions data were analyzed using a mixed model approach, with the fixed effect parameter being ethanol content. Emission measurements were tran sformed using the natural logarithm before input into the model, which is a standard practice in analysis of this type of data in order to mitigate issues with data variability and skew. Results shown in Table 3 indicate that

a 10% ethanol blend (E10) did not have a statistically significant effect (at a p = 0.05 level) on NMHC or NOx emissions relative to gasoline containing no ethanol (E 0) at either test temperature. The p

- value refers to the significance level of the statistical comparison. In most
sc ientific studies of physical phenomena , a result (such as a difference between two treatments ) is accepted as true or valid only if the significance level is p = 0.05 or less, suggesting relative safety from accepting a result which may have occurred only by chance

. Since none of the emission comparisons evaluated here had p

- values at 0.05 or below, we interpret this to mean there is no difference in emissions between the E0 and E10 fuels.
Figure 3 depicts the data after removal of outliers, with calculat ed means and 95% confidence intervals

. The confidence interval describes the range in which the true mean of all such emission results would fall with 95% likelihood, which gives an indication of the precision of the calculated mean value shown.**Table 1 . Test vehicle fleet summary.** 

**MAKE BRAND**  **MODEL (all 2008 model year) ENGINE**  Chrysler Dodge Caliber 2.4L I4 Chrysler Dodge/Chrysler Caravan/Town&Country 3.3L V6 Chrysler Jeep Liberty 3.7L V6 Ford Ford Focus 2.0L I4 Ford Ford 500/Taurus/Freestyle 3.0L V6 Ford Ford F150 5.4L V6 Ford Ford/Mercury Explorer/Mountaineer 4.0L V6 GM Buick/GMC/Saturn Enclave/Acadia/Outlook 3.6L V6 GM Chevrolet Cobalt/HHR 2.4L I4 GM Chevrolet Impala 3.5L V6 GM Chevrolet/GMC Avalanche/Silverado 5.3L V8 Honda Honda Civic 1.8L I4 Honda Honda Accord 2.4L I4 Honda Honda Odyssey 3.5L V6 Nissan Nissan Altima 2.5L I4 Toyota Toyota Corolla 1.8L I4 Toyota Toyota Camry 2.4L I4 Toyota Toyota Sienna 3.3L V6 Toyota Toyota Tundra 4.0L V6

**Table 2. Test fuel property summary.**

**E0 E10**  Ethanol vol % D5599 <0.1 9.35 T50 °F D86 215 209 T90 °F D86 324 319 RVP psi D5191 9.17 9.05 Aromatics vol % D1319 29.3 22.9 Olefins vol % D1319 6.4 5.7 Benzene vol % D3606 0.48 0.49 Sulfur ppm D5453 23 23 RON

- D2699 93.4 93.7 MON

- D2700 83.5 84.9 (R+M)/2

- - 88.5 89.3 **Parameter Units**  **Method Test Fuel** 

**Table 3** 

**. Summary of Statistical**  **Analysis of Emission Tests**

**. Emission**  **Test Temperature Percent Difference**  **P-value*** **(deg.F) (E10 vs. E0)**  NOx (composite result) 50 -12.87 0.64 NOx (composite result) 75 -7.59 0.94 NMHC (composite result) 50 -3.93 0.97 NMHC (composite result) 75 -12.96 0.09

* P

- value refers to the significance level of the statistical comparison. In most studies of physical phenomena , a result is accepted as true or valid only if the sig nificance level is p = 0.05 or less, suggesting relative safety from accepting a result which may have occurred only by chance

. We interpret this to mean no significant differences were found, and thus n o emission difference between E0 and E10 fuels

.**Figure 1**

**. LA92 test cycle** 

**.**

0 10 20 30 40 50 60 70 80

0 200 400 600 800 1000 1200 1400 1600 **Time (seconds) Speed (mph)**  Phase 1 300s 1.19mi Phase 2 1135s 8.63mi Phase 3 300s 1.19mi

**Figure 2**

**. NMHC Composite Means**  **(Blue Dots) and 95%**  **Confidence Intervals**  **(Vertical Lines) after outlier removal** 

**.**

0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09

50_E0 50_E10 75_E0 75_E10 **Temperature (50, 75) and EtOH Level (E0, E10) g** 

**p e**  **r**

**m i** **Figure 3**

**. NOx**  **Composite Means (Blue Dots) and 95%**  **Conf idence**  **Intervals (Vertical Lines)**  **after outlier removal.**

0.005 0.010 0.015 0.020 0.025 0.030 0.035 0.040 0.045

50_E0 50_E10 75_E0 75_E10 **Temperature (50, 75) and EtOH Level (E0, E10) g** 

**p e**  **r**

**m i**