NREL/CP-540-40015. Posted with permission. 

Presented at the Powertrain and Fluid Systems 

Conference and Exhibition, October 2006, Toronto, Canada 2006-01-3280 

Effect of Biodiesel Blends on Diesel Particulate Filter 

Performance 

Aaron Williams, Robert L. McCormick, R. Robert Hayes, John Ireland 

National Renewable Energy Laboratory 

Howard L. Fang 

Cummins, Inc. 

Copyright © 2006 Society of Automotive Engineers, Inc.

ABSTRACT 

Tests of ultra-low sulfur diesel blended with soy-biodiesel 

at 5% and 20% were conducted using a 2002 model year 

Cummins ISB engine (with exhaust gas recirculation) 

that had been retrofitted with a passively regenerated 

catalyzed diesel particulate filter (DPF). Results show 

that on average, the DPF balance point temperature 

(BPT) is 45°C and 112°C lower for B20 blends and neat 

biodiesel, respectively, than for 2007 certification diesel 

fuel. Biodiesel causes a measurable increase in 

regeneration rate at a fixed steady-state condition, even 

at the 5% blending level. The data show no significant 

differences in NOx emissions for these fuels at the 

steady-state regeneration conditions, suggesting that 

differences in soot reactivity are responsible for the 

observed differences in BPT and regeneration rate. Soot 

from the various fuels was characterized by determining 

the fuel and lubricant fractions of the soluble organic 

fraction, elemental and organic carbon content, 

amorphous carbon/graphitic carbon ratio by Raman 

spectroscopy, carbon/oxygen ratio by energy dispersive 

x-ray analysis, and reactivity in oxygen by TGA. Results 

indicate a much more disordered soot structure, 

containing higher levels of oxygen as biodiesel is 

blended into the diesel fuel. The soot produced from 

biodiesel and blends is much more reactive in oxygen 

than diesel soot. It is concluded that the lower balance 

point temperature and higher DPF regeneration rates for 

biodiesel containing fuels are observed because the soot 

generated from these blends is more reactive. 

INTRODUCTION 

Biodiesel is a renewable fuel derived from vegetable oil, 

animal fat, or waste cooking oil and consists of the 

methyl esters of fatty acids. It is typically used as a 

diesel blending component at levels of 20 volume 

percent or lower. A resource assessment indicates that 

biodiesel has the potential to displace 5% or more of 

petroleum diesel over the next decade [1]. A life cycle 

analysis indicates that biodiesel is a highly renewable 

fuel, and that use of B20 results in a 19% reduction in life 

cycle petroleum consumption [2]. The United States 

Environmental Protection Agency (EPA) has reviewed 

biodiesel emissions data for heavy-duty engines 

published up through about 2000 [3]. For transient 

engine dynamometer testing, the average emission 

changes for B20 versus petroleum diesel were +2.0% for 

NOx, -10.1% for PM, -11.0% for carbon monoxide (CO), 

and -21.1% for total hydrocarbons (THC). However, 

closer scrutiny of the available data suggests that 

increasing NOx is not necessarily a general phenomenon 

for biodiesel at the B20 level, and that NOx emissions 

depend upon engine duty cycle or mode as well as 

engine technology [4]. More recently data were 

published reporting the testing of two newer engines 

equipped with EGR and meeting the 2004 emission 

standards, with B20 vs. ultra-low sulfur diesel (ULSD) 

fuel. This study found, on average, a 25% reduction in 

PM emissions for B20 [5], but NOx increased by nearly 4 

%. 

In 2007, new emission standards for on-road heavy-duty 

diesel engines will begin to phase in. Most relevant to 

this work, beginning with the 2007 model year the 

particulate matter emission standard will be lowered from 

0.1 g/bhp-h to 0.01 g/bhp-h. This lowering of PM 

emissions by a factor of 10 is enabled by the introduction 

of diesel fuel containing a maximum of 15 ppm sulfur 

(ULSD) beginning in June of 2006 and the use of diesel 

particulate filters. In a DPF, soot particles are trapped on 

a filter. In catalyzed DPF systems such as that tested 

here, the soot is then burned by reaction with NO2. The 

role of NO2 as an oxidizer is critical to catalyzed DPF 

performance and DPFs typically contain a precious metal 

catalyst upstream of the ceramic filter, where NO is 

converted to NO2. This NO2 is a more aggressive 

oxidizer of soot at low temperatures than is oxygen, and 

thus can control the soot oxidation rate. Thus, a small 

increase in NOx emissions (mainly NO) observed for B20 

during transient testing could have significant 

consequences for the performance of B20 with DPFs. 

1
Some published information is available on the 

performance of DPFs with biodiesel and biodiesel 

blends. Testing of B20 and several other fuels with 

various aftertreatment and engine configurations [6] has 

been reported. The use of a catalyzed DPF produced a 

factor of 10 reduction in PM emissions relative to the 

base case. No PM emission advantage was observed 

for B20 with a DPF installed. No engine-out emissions 

were reported for B20 in this study. Additionally, 2007 

compliant procedures for PM emission measurement do 

not appear to have been used. However, Boehman and 

coworkers [7] have recently shown that blending of 20% 

biodiesel into diesel fuel can significantly lower balance 

point temperature (BPT). They present results showing 

that this is not caused by increased availability of NO2, 

but by inherent differences in soot reactivity for different 

fuels. This was confirmed by thermogravimetric analysis 

wherein soot produced in an engine from different fuels 

was burned under identical conditions. Soot 

characterization by electron microscopy suggested that 

the cause of this increased reactivity is a more highly 

disordered soot nanostructure for B20 blends such that 

the soot is more reactive or reactive at lower 

temperatures. More recent results presented by 

Boehman [8] suggest that changes in nanostructure are 

not the cause of increased reactivity, but rather the 

introduction of highly reactive surface oxygen sites when 

the soot is produced from B20. 

Here we examine the impact of biodiesel and biodiesel 

blends on balance point temperature, filter regeneration 

rate, and transient emissions using a modern (2004 

compliant) engine and state of the art (2007/2010 

compliant) emissions measurement system. 

EXPERIMENTAL SETUP 

The test setup consisted of a 2002 model year 5.9L 300 

hp Cummins ISB, equipped with a diesel particle filter 

(DPF). Properties of the test engine are shown in Table 

1. The engine employs cooled high-pressure EGR, a 

variable geometry turbocharger, electronic control, and 

high-pressure common rail direct fuel injection, designed 

and calibrated to meet the 2004 U.S. heavy-duty 

emissions standards. 

The DPF is a 12 L catalyzed diesel particle filter 

employing Catalyzed Continuously Regenerating 

Technology (CCRTTM) provided by Johnson Matthey, a 

passively regenerated system. The CCRTTM filter is a 

diesel oxidation catalyst followed by a wall-flow catalyzed 

soot filter. It is used in applications with average exhaust 

temperatures as low as 200°C - 250°C. The DPF is 

mounted 152 cm from the engine turbo flange outlet. 

The DPF was instrumented for inlet and outlet 

temperatures and pressures as well as differential 

pressure. Temperatures were measured with K-type 

thermocouples mounted 8 cm from the face of the precatalyst on the inlet side and 8 cm from the face of the 

DPF on the outlet side. Inlet and outlet pressures as well 

as differential pressure were measured from the same 

location. The overall setup and relative location of all 

instrumentation is illustrated in Figure 1. In addition, 

engine and emissions sampling systems were 

instrumented for measurement of all other critical 

temperatures and pressures. 

Table 1. Test engine specifications 

Cummins ISB 

Serial Number 56993170 

Displacement, L 5.9 

Cylinders 6 

Rated Power, kW 224 at 2500 rpm 

Rated Torque 895 N-m at 1600 rpm 

Bore x Stroke 10.2x12 cm 

Compression Ratio 16.5:1 

Fuel System Common Rail 

Intake Restriction, kPa 4.47 

Exhaust Backpressure, kPa 7.95 

Figure 1. Experimental Setup 

The engine was mounted to a DC electric engine 

dynamometer at NREL’s Renewable Fuel and Lubricant 

(ReFUEL) laboratory. ReFUEL’s engine dynamometer is 

part of a fully functional test cell capable of steady state 

or transient testing for emissions and fuel consumption. 

The ReFUEL emission measurement system is based 

on the full scale dilution method with Constant Volume 

Sampling (CVS) for mass flow measurement. Gaseous 

emissions, including CO2, NOx, THC and CO are 

measured continuously. Particulate matter (PM) 

emissions are measured based on a gravimetric system, 

in which samples are collected onto 47 mm Teflon 

membrane filters and then weighed with a microbalance 

in a clean room environment. 

Test fuels included 2007 certification diesel and various 

biodiesel blends made from a soy biodiesel feedstock. 

The soy biodiesel was S15 grade and met the 

requirements of ASTM D6751. Fuel properties for the 

2007 certification ULSD and the neat biodiesel are listed 

in Table A-1 in the Appendix. 

2
PROCEDURES AND RESULTS 

ESTIMATION OF PARTICLE LOADING 

In addition to fuel effects, performance of the DPF could 

be affected by the level of particulate loading. Thus, 

experiments were conducted to understand how to 

repeatedly preload the DPF with the same amount of 

particulate, and how to quantify that amount. In all cases 

the 12 Liter DPF was loaded to approximately 1.5 g/L to 

approximate typical in-use loading levels. However, the 

amount of time necessary to produce the total 18 grams 

of PM at the 2000 rpm 20 ft-lb preload condition is 

different for each fuel. A series of experiments were 

conducted to determine the rate of PM production by the 

engine for each fuel at the preload condition. The results 

of these experiments were then used to determine the 

proper load period for all subsequent BPT and 

regeneration rate testing. In addition, a method of 

weighing the DPF before and after loading was 

developed to further confirm the total mass collection. 

Particulate Matter Rate Study

Testing was conducted to determine the total output of 

PM from the engine when operating at the 2000 rpm 20 

ft-lb preload condition for a 340 minute period. Without 

the DPF installed, engine-out PM samples were collected 

every 20 minutes for the entire 340 minute duration. 

Samples were collected onto 47 mm Teflon membrane 

filters at a sample flow rate of 43 L/min for 20 minutes 

each. The filters were then weighed to determine the 

total PM production from the engine. This test was 

conducted for 2007 certification diesel (2007 Cert), B20 

and B100, the results of which are shown in Figure 2. 

Assuming that the DPF captures and stores all of the PM 

at the preload condition, total collection of 18 grams (1.5 

g/L) would take 332, 314 and 239 minutes for B100, B20 

and 2007 Cert respectively. 

DPF Loading by Weight

The preload condition of the DPF was further confirmed 

by taking fully regenerated (clean) and loaded weights of 

the DPF. The DPF weighed 17.2 kg compared to the 18 

grams of PM being collected, illustrating the degree of 

accuracy necessary. An electronic balance with a 

resolution of 0.1 grams was used. Initially the DPF was 

allowed to equilibrate in an environmental chamber for a 

minimum of 12 hours before weighing. Temperature and 

humidity were controlled to 20°C with a relative humidity 

of 47%. When weighing the DPF during this 12 hour 

Figure 2. PM rate study results for B100, B20 and 2007 

Certification Diesel 

stabilization period, it was found that the DPF would 

immediately begin gaining weight in the relatively humid 

environment and eventually stabilize before the twelfth 

hour. The DPF appeared to absorb moisture even with 

substrate temperatures as high as 800°F. Overall, the 

loaded DPF would gain as much as 13 grams of 

moisture before stabilizing. However, it was discovered 

that a clean DPF was more hygroscopic than a loaded 

DPF, gaining as much as 21 grams of moisture. Thus, 

accurate measurements of loaded mass could not be 

determined by taking the difference in clean and loaded 

DPF weights, each of which was taken after equilibration 

in a humid environment. 

The second iteration of a weighing technique consisted 

of weighing the DPF in a dry room environment. In this 

case, with relative humidity controlled to below 20%, the 

DPF still gained weight due to moisture, however, not as 

quickly. It was decided that the best technique for 

weighing was to remove the DPF as quickly as possible 

following engine operation and take immediate 

measurements in the dry room conditions. This 

technique yielded repeatable DPF loading 

measurements between 1.3 and 1.7 g/L compared to the 

target 1.5 g/L predicted by the PM rate studies. 

BALANCE POINT TEMPERATURE 

The balance point temperature is defined as the DPF 

inlet temperature at which the rate of particle oxidation 

approximately equals the rate of particle collection. At 

the balance point temperature during steady-state 

operation, the DPF should not experience a net gain or 

loss of particulate matter and consequently the 

differential pressure across the DPF should not change. 

A series of balance point temperature tests were 

conducted to compare the operation of a DPF on 2007 

certification diesel, B100, and a B20 blend. The balance 

point temperature was determined with the following test 

sequence and is illustrated in Figure 3. 

1. The DPF was completely regenerated by 

operating at near rated power (2500 rpm and 

575 ft-lbs) for 120 minutes. 

3
2. The DPF was then preloaded with PM at 2000 

rpm and 20 ft-lbs over the appropriate amount of 

time to achieve an approximate 1.5 g/L loading 

of particulate matter on the DPF. 

3. The preloaded DPF was then operated at 1700 

rpm while torque was increased to achieve 

specified exhaust temperatures. The DPF 

pressure drop was monitored continuously to 

determine slope of the increase or decrease of 

the differential pressure across the DPF at a 

given inlet temperature. 

4. This sequence was repeated for 2007 

certification diesel, B100 and B20 fuels for 

determination of BPT at 1700 rpm. 

Figure 3. Balance point temperature test DPF differential 

pressure 

The balance point temperature is determined by 

analyzing the slope of the differential pressure for each 

of the temperature steps. If the slope is positive 

(backpressure is increasing) then it is assumed that the 

DPF is collecting particulate matter. Once the slope 

becomes negative (backpressure is decreasing) that 

temperature is above the balance point temperature, as 

previously defined. The balance point temperature 

determination is made by plotting the slope of the 

differential pressure versus the DPF temperature for 

each of the steps. A linear curve fit is made between the 

two steps where differential pressure slope transitions 

from a positive to a negative value. The point where the 

curve fit crosses the Y-intercept is determined as the 

best estimate of the balance point temperature. In order 

to understand variability of the testing method, two 

repeats of the balance point temperature test were 

completed for 2007 certification diesel and B20, and 

three repeats for B100. In the case of 2007 certification 

fuel, additional torque steps were added in order to move 

sufficiently beyond the balance point temperature. 

Figure 4 shows the resulting balance point temperature 

windows for each of the fuels. On average, the balance 

point temperature is 45°C lower than 2007 certification 

diesel for B20 blends and 112°C lower for neat biodiesel. 

REGENERATION RATE 

The regeneration rate testing is similar to balance point 

temperature testing in that the DPF is fully regenerated 

and preloaded to approximately 1.5 g/L. However, rather 

than stepping through different torques at 1700 rpm, the 

engine moves directly to a single, relatively high torque 

(high temperature) operating point. This test method is 

illustrated in Figure 5. This method provides a potential 

advantage of comparing regeneration behavior between 

fuels at the same approximate DPF preload conditions 

(grams/Liter) and same high load steady-state operating 

point. This contrasts with the stepped BPT measurement 

method, which allows for different loading to occur during 

the “steps” following preload and prior to reaching the 

BPT. 

Figure 4. Balance point temperature test results for 

B100, B20 and 2007 Certification Diesel 

Figure 5. Regeneration rate test DPF differential 

pressure 

Testing was conducted with 2007 certification diesel, B5 

and B20 with two repeats for each fuel. Once the DPF 

had been preloaded the engine was then operated at the 

higher temperature point (1700 rpm and 250 ft-lbs) for 60 

minutes. This allowed enough time for DPF temperature 

to stabilize. In each case, the DPF temperature at the 

active regeneration point stabilized between 348°C and 

357°C. In general, DPF inlet temperatures were lower 

with higher blend ratios of biodiesel. DPF differential 

pressures also varied from test to test, either as a 

consequence of the slight temperature differences or 

relative differences in the amount of particle loading. At 

the stabilized regeneration point, DPF differential 

pressures ranged between 48.3 cm of H2O and 52.1 cm 

of H2O. 

4
Results for regeneration rates are shown in Figure 6. 

This plot shows the normalized DPF differential pressure 

for the final 15 minutes of steady state operation at the 

active regeneration point. DPF differential pressures are 

normalized to show relative differences in performance 

for each of the fuels. As the plot shows, the differential 

pressure slope for 2007 certification fuel is slightly 

positive for repeated runs at 1700 rpm, 250 ft-lb 

operating condition with temperatures around 354°C. 

This is consistent with previous testing that showed a 

balance point temperature somewhere between 359°C 

and 364°C for this fuel. The plot also illustrates that both 

biodiesel blends at the B5 and B20 level show 

measurable decreases in DPF differential pressure at 

the same operating condition with similar amounts of 

DPF preloading. The slope of the differential pressure 

decrease increases with biodiesel content. These test 

results show that when fueled with biodiesel blends, PM 

appears to measurably oxidize more quickly than when 

fueled with certification diesel fuel (even down to the B5 

level). Increased levels of biodiesel in the fuel appear to 

increase the rate of DPF regeneration at a given engine 

operating condition. 

Figure 6. Regeneration rate test results for B20, B5 and 

2007 Certification Diesel

AVAILABILITY OF NO2 FOR DPF REGENERATION 

Catalyzed DPFs use NO2 as the oxidizer of trapped soot. 

Thus, increased NOx from biodiesel blends could 

potentially be the cause of the observed higher 

regeneration rates. Table 2 shows brake specific NOx

levels at the regeneration condition for each fuel. For 

this experiment, differences in NOx levels between 2007 

certification diesel and the biodiesel blends are not 

statistically significant (at alpha = 0.05). This suggests 

that differences in regeneration rates are not primarily 

due to differences in the availability of NO2 as a soot 

oxidizer, although higher NO2 availability may play a 

secondary role for B20. 

Table 2. NOx Levels at Regeneration Condition of 1700 

rpm and 250 ft-lb Torque (p-value for comparison of 

certification fuel NOx to biodiesel blend NOx) 

2007 Cert B5 B20 

Run 1 NOx (g/bhp-hr) 1.96 2.00 2.13 

Run 2 NOx (g/bhp-hr) 2.06 1.93 2.16 

Average NOx 2.01 1.97 2.15 

p-value -- 0.445 0.078 

The availability of NOx at each step in the balance point 

temperature test is illustrated in Figure 7 for each of the 

three test fuels. B100 NOx levels (g/bhp-hr) trend higher 

at temperatures above 280°C. However, at the balance 

point temperature for B100 (250°C), the availability of 

NOx is approximately the same as petroleum based 

diesel or B20. The same is true for NOx levels at the 

BPT for B20 (317°C), once again indicating that reactivity 

of the soot, rather than availability of NO2, is the primary 

factor in the determination of the balance point 

temperature for each test fuel. It should be noted that 

speciation of NOx for NO and NO2 components was not 

performed. Biodiesel blends could also impact the 

NO/NO2 split, which may have an impact on efficiency of 

the DPF. Also of note is the relative difference in the 

NOx/PM ratio for each test fuel. Because of lower 

engine out PM for biodiesel and the higher soluble 

organic fraction, the biodiesel NOx/Soot ratio will be 

much higher than that of 2007 certification fuel. The 

impact of this ratio on balance point temperature and 

regeneration rate was not explored in this study. 

Figure 7. NOx levels at BPT steps for 2007 Certification 

Diesel, B20 and B100 

TRANSIENT EMISSIONS TESTING 

Baseline emissions over multiple hot start heavy-duty 

transient tests were measured for the 2007 certification 

fuel and a B20 blend. These tests were conducted with 

and without the DPF for both fuels to confirm operation 

of the filter and to determine reduction efficiencies of all 

regulated pollutants. Individual test results for each 

repeated run are shown in Table A-2. Table 3 shows the 

5
percent changes in emissions and fuel economy for each 

test configuration. 

Table 3. Percent change in emissions and fuel economy 

(nd = non-detectable differences with 95% confidence) 

PM THC CO NOx BSFC 

Cert w/ DPF vs 

Cert w/o DPF -99% -99% -97% nd +1% 

B20 w/ DPF vs 

B20 w/o DPF -99% -99% -98% nd +1% 

Cert vs B20 w/o 

DPF -24% -50% -22% +4% +3% 

Cert vs B20 w/ 

DPF -27% -74% nd +4% +3% 

Before installation of the DPF, the B20 blend achieved a 

24% PM reduction relative to 2007 Cert, as shown in 

Figure 8. Following DPF installation, PM emissions were 

reduced by 90% for 2007 Cert and B20. B20 combined 

with the DPF still showed a statistically significant 

(p<0.05) reduction in PM of 27% relative to 2007 Cert 

with DPF. 

 

Without the DPF, biodiesel reduced emissions of both 

THC and CO by 50% and 22%. In the case of both fuels 

the catalyzed DPF reduced THC and CO emissions by 

97% to 99%, to almost undetectable levels. NOx

emissions increased for the biodiesel blend by 4% on 

average without the DPF compared to ULSD runs. DPF 

installation caused NOx emissions to increase by 1%. 

The biodiesel blend produced a 3% (p<0.001) increase 

in brake specific fuel consumption, consistent with the 

lower energy content of biodiesel, as shown in Table A-1. 

Installation of the DPF produced a 1% fuel economy 

penalty for both fuels (p<0.001). 

Figure 8. Transient test particulate matter emissions 

SOOT CHARACTERIZATION RESULTS 

Soot Collection Methods

Particle samples used for soot characterization were 

collected at the engine preload condition (2000 rpm 20 ftlbs) for each test fuel. Without the DPF installed, dilute 

exhaust PM samples were collected onto 47 mm filters 

using methods consistent with CFR Title 40 Part 86 

Subpart N. A butterfly valve was used to simulate 

exhaust back pressures similar to those created by the 

DPF. Approximately 46 mg were collected onto Pallflex 

Quartz filters and 10 mg were collected onto Teflon 

membrane filters. Bulk soot was collected directly from a 

preloaded DPF by back-flushing the filter with high 

pressure air into a collection canister. The DPF was first 

loaded by operating the engine at the preload condition 

for the time appropriate to achieve the 1.5 g/L loading. 

Using this method, approximately 1 gram was collected 

for 2007 certification diesel and B100. 

Fuel and Lubricant Fraction of SOF

The soluble organic fraction (SOF) of PM samples was 

extracted using supercritical CO2. The extracted 

hydrocarbon was delivered into an ODS trap (Agilent) 

and rinsed with CS2. The CS2 solution was injected into 

a gas chromatograph (HP 5880A) using a packed 

column (Chromosorb PAW) and a flame ionization 

detector (FID). The carrier gas was N2 and the heating 

rate is set at 10°C/min for the temperature range from 

35°C to 350°C. The SOF elutes as two major bands 

corresponding to fuel at roughly 12 minutes and lubricant 

as a broad band centered around 17 minutes. The fuel 

light end components, normally eluting before 10 

minutes in the chromatogram, are missing for all 

samples studied, suggesting that the light portion of the 

fuel has evaporated. Based on the ratio of the fuel and 

oil peak areas, we can determine the lubricant fraction in 

the SOF and the data are shown in Table 4. 

PM samples collected on both quartz and Teflon 

membrane filters were examined for 2007 certification 

diesel, B20 and B100. For 2007 Cert the major SOF 

component is lubricant regardless of the filter type. 

When biodiesel is used, roughly 25% of the SOF can be 

attributed to the fuel. The contribution of the fuel is even 

larger when Teflon membrane filters are used. 

Table 4. Lubricant Fraction of the PM Soluble Organic 

Fraction (SOF) Measured by GC 

Filter Type/Fuel Quartz Teflon Membrane 

2007 Cert 95% 96% 

B20 71% 78% 

B100 75% 50% 

Organic Carbon/Elemental Carbon Ratio

The ratio of organic and elemental carbon was 

measured by a thermal-optical carbon aerosol analyzer. 

The PM sample is placed in a quartz oven and is heated 

under helium with a stepped temperature ramp up to 

900°C. Under this condition, all organic compounds are 

desorbed, pyrolyzed, and converted into CO2. The CO2

is swept through a heated nickel catalyst and converted 

into methane which can be quantified with a flame 

ionization detector. After the initial temperature ramp for 

6
organic carbon measurement, the oven is cooled to 

600°C and the flow is switched to a helium/oxygen. A 

second temperature ramp is then initiated in the oxidizing 

gas stream to oxidize the elemental carbon. The 

elemental carbon is quantified in the same manner as 

the organic carbon. The elemental carbon can be also 

quantified by optical absorption detection. 

As shown in Table 5, the OC/EC ratio follows a general 

trend of B100 > B20 > 2007 Cert. This indicates that the 

PM generated by biodiesel contains more organic carbon 

and that organic carbon content is higher with increasing 

biodiesel content. 

Table 5. OC/EC Ratio of Various PM Samples 

Fuel 

OC 

μg/cm2

EC 

μg/cm2

OC/EC 

2007 Cert 206.37 38.11 5.42 

2007 Cert 219.07 31.79 6.89 

B20 419.94 17.63 23.82 

B100 414.54 15.25 27.19 

Raman Spectroscopy 

Raman spectroscopy is unique in characterizing the long 

range interactions and the order-disorder effects in 

carbonaceous materials. Pristine graphite crystals only 

show two bands in first-order Raman spectrum, at 42 

and 1578 cm-1. The 1578 cm-1 band is referred to as the 

graphitic band or G-band. As the graphite crystal is 

ground to destroy the ordering, a second band, referred 

as the amorphous band or disordered band, or D-band, 

begins to appear around 1340 cm-1. For carbonaceous 

materials such as soot or coal, the D-band is relatively 

broad and sensitive to the ordering of the carbon 

structure. Both maturation and oxidation level of PM 

affect the ordering of the carbon structure. The 

maturation, in morphological sense, is the collapse of 

small aromatic domains with 1~4 rings into a 

configuration containing larger ring number domains. 

Besides the growth of a two-dimensional domain size, 

the layer-to-layer orientation also plays a determining 

role for long range ordering [9, 10]. 

Two micro-Raman units were used to examine the soot 

samples: a Dilor XY800 Raman microprobe equipped 

with Ar+

 laser (514.5nm) and a Rennishaw with a He-Ne 

laser (632.8nm). Both laser wavelengths were focused 

on the sample through a microscope with a 50x or 100x 

objective lens and the scattered light collected through a 

holographic filter and detected via a CCD detector. 

Figure 9 shows a comparison of Raman spectra of PM 

samples generated from 2007 certification diesel, B20 

and B100. The graphite-like G-band is located around 

1586 cm-1 with a bandwidth of about 100 cm-1. The 

disordered D-band is located around 1349 cm-1 with a 

much wider bandwidth >250 cm-1. Multiple Raman 

spectra were taken for each sample at various locations 

to avoid inhomogeneity in the samples. The average 

ratio G/D and the corresponding standard deviation are 

listed in Table 6. 

800

1800

2800

3800

4800

5800

6800

7800

800 1000 1200 1400 1600 1800

cm-1

Raman Intensity

B0

B20

B100

Figure 9. Raman spectra of the PM samples 

As shown in Figure 10, the general trend for the G/D 

ratio is to decrease with biodiesel blend level even 

though the standard deviation is suddenly increased for 

PM generated by B100, indicating much greater variation 

in domain structure. This is consistent with previously 

published data [7] showing much greater disorder for 

biodiesel soot. This trend is generally true regardless 

which Raman unit is being used. The slight ratio variation 

can be attributed to background difference caused by the 

different laser excitation wavelengths. 

Table 6. G/D Ratio Measured by Rennishaw MicroRaman with 632.8 nm Excitation 

Fuel G/D 

Standard 

Deviation 

2007 Cert (Quartz) 0.836 0.057 

B20 (Quartz) 0.756 0.023 

B100 (Quartz) 0.586 0.175 

2007 Cert (Teflon) 0.823 0.007 

B20 (Teflon) 0.836 0.026 

B100 (Teflon) 0.66 0.022 

7
Rennishaw data w ith 632.8 nm excitation

0.2

0.4

0.6

0.8

1

-10 10 30 50 70 90 110

[Biodiesel] % in ULSD

G/D Ratio

J-Y data w ith 514.5 nm excitation

0.6

0.8

1

1.2

-10 10 30 50 70 90 110

[Biodiesel]% in ULSD

G/D Ratio

Figure 10. The dependence of the Raman G/D ratio on 

biodiesel blend level 

X-ray Spectroscopy

Energy-dispersive x-ray spectroscopy (EDS) is based on 

measurement of the characteristic x-rays generated from 

a sample irradiated with high-energy electrons. EDS 

measurements were made with a Hitachi 4100 Field 

Emission scanning electron microscope with a Gresham 

Sirius EDS detector. The excitation voltage was 5 KV. 

Carbon to oxygen ratios determined for soot samples 

produced from 2007 certification diesel and from B100 

were 25.34 and 20.34, respectively. This indicates that 

the B100 soot contains roughly 20% to 25% more 

oxygen than soot from 2007 certification diesel. 

Thermogravimetric Analysis

Thermogravimetric measurement was performed with a 

Thermal Analysis TGA Q500 unit. All samples were 

originally collected on quartz filters. The sample was cut 

into small pieces stacked in the weighing pan. Thus, the 

majority of the sample weight is due to the quartz 

substrate. The heating rate was 100°C/min for 

temperatures below 400°C. The rate was decreased to 

30°C/min when temperature reached 400°C (at the 

location marked ↑ in Figure 11). At 400°C, the purge 

gas was switched from N2 to O2. So at temperatures 

below 400°C, we observed weight loss from evaporation 

and devolatilization, while above 400°C weight loss was 

caused by combustion. 

Figure 11 compares TGA results for three PM samples 

from the different fuels. PM derived from B20 and B100 

contains a much greater fraction that is volatile, 

consistent with the higher organic carbon content. 

Above 400°C, there is a significant difference in the 

combustion temperature for these samples. For 2007 

certification diesel, combustion occurs between about 

650°C and 680°C, while the temperature for B20 is 

shifted to 550°C-580°C. The B100 sample shows a 

slightly higher conversion temperature, but the 

experiment was not precise enough to determine if there 

is a real difference between B20 and B100. 

0.89

0.91

0.93

0.95

0.97

0.99

1.01

0 100 200 300 400 500 600 700 800

Temperature (C)

(Weight Loss)%

B0

B20

B100

O2 feed

Figure 11. Thermogravimetric analysis results 

CONCLUSIONS AND RECOMENDATIONS 

Results show that on average, the balance point 

temperature is 45°C lower than 2007 certification diesel 

for B20 blends and more than 112°C lower for B100. 

Filter regeneration rate measurements indicate that 

biodiesel causes a measurable increase in regeneration 

rate, even at the 5% blending level. Transient emissions 

tests show a 24% particulate matter (PM) reduction for 

B20 without the DPF installed. Installation of the DPF 

caused PM emissions to drop by more than a factor of 

10 for both fuels. Use of B20 with the DPF shows a 

statistically significant reduction of 27% below the 

petrodiesel+DPF level. The use of B20 caused a 3% 

increase in fuel consumption, consistent with the lower 

energy content of this fuel. Installation of the DPF 

caused a 1% fuel economy penalty for both 2007 

certification diesel and B20. 

An examination of NOx availability at the BPT and DPF 

regeneration conditions suggests that increased NOx

emissions from biodiesel and biodiesel blends are not 

responsible for the higher regeneration rate or lower 

BPT. Detailed chemical and spectroscopic 

characterization results point to the higher degree of 

disorder in the soot structure and higher oxygen content 

as the main factors responsible for the observed effects. 

This is confirmed by TGA combustion tests. The results 

8
of this study therefore confirm those of Boehman [7, 8] 

and indicate practical implications in terms of DPF 

regeneration and the potential for additional PM 

reduction. 

The significant lowering of balance point temperature 

and increase in regeneration rate might allow passive 

DPFs to be used in lower temperature engine duty 

cycles, avoiding or reducing the need for actively 

regenerated filters and their associated fuel economy 

penalty. This hypothetical fuel economy benefit has yet 

to be demonstrated and will be the subject of future 

research. 

ACKNOWLEDGEMENTS 

This work was supported by the United States 

Department of Energy, FreedomCAR and Vehicle 

Technologies Program, the National Biodiesel Board, 

and by Cummins, Inc. 

REFERENCES 

1. Tyson, K.S.; Bozell, J.; Wallace, R.; Petersen, E.; 

Moens, L. Biomass Oil Analysis: Research Needs 

and Recommendations. NREL/TP-510-34796. 

Golden, CO: National Renewable Energy Laboratory, 

June 2004. 

2. Sheehan, J.; Camobreco, V.; Duffield, J.; Graboski, 

M.; Shapouri, H. An Overview of Biodiesel and 

Petroleum Diesel Life Cycles. NREL/TP-580-24772. 

Golden, CO: National Renewable Energy Laboratory, 

May 1998. 

3. United States Environmental Protection Agency. A 

Comprehensive Analysis of Biodiesel Impacts on 

Exhaust Emissions. EPA420-P-02-001. Draft 

Technical Report. 2002. 

4. McCormick, R.L., J.D. Ross, M.S. Graboski “Effect 

of Several Oxygenates on Regulated Emissions from 

Heavy-Duty Diesel Engines” Environ. Sci. Technol., 

Vol 31, 1997, p. 1144. 

5. McCormick, R.L.; Tennant, C.; Hayes, R.R.; Black, 

S.; Williams, A.; Ireland, J.; McDaniel, T.; Frailey, M.; 

Sharp, C.A. Regulated Emissions from Biodiesel 

Tested in Heavy-Duty Engines Meeting 2004

Emission Standards. 2005-01-2200. Society of 

Automotive Engineers. 2005. 

6. Frank, B.P.; Tang, S.; Lanni, T.; Rideout, G.; 

Beregszaszy, C.; Meyer, N.; Chatterjee, S.; Conway, 

R.; Lowell, D.; Bush, C.; Evans, J. A Study of the 

Effects of Fuel Type and Emission Control Systems 

on Regulated Gaseous Emissions from Heavy-Duty 

Diesel Engines. 2004-01-1085. Society of 

Automotive Engineers. 2004. 

7. Boehman, A.L.; Song, J.; Alam, M. “Impact of 

Biodiesel Blending on Diesel Soot and the 

Regeneration of Particulate Filters” Energy & Fuels. 

Vol 19, 2005, p. 1857. 

8. Boehman, A.L. “Effect of Alternative Fuels on Soot 

Properties and Regeneration of Diesel Particulate 

Filters.” 2005 Biodiesel Technical Workshop, 

November 2005, Denver Colorado. 

9. Kelemen, S.; Fang, H.L. “Maturity Trends in Raman 

Spectra from Kerogen and Coal.” Energy & Fuels. 

Vol. 15, 2001, p. 653. 

10. Fang, H.L.; Lance, M. Influence of Soot Surface 

Changes on DPF Regeneration. 2004-01-3043. 

Society of Automotive Engineers. 2004. 

ACRONYMS AND ABBREVIATIONS 

ASTM American Society for Testing and Materials 

BSFC Brake specific fuel consumption 

B100 100% biodiesel 

B20 20% biodiesel, 80% petrodiesel 

B5 5% biodiesel, 95% petrodiesel 

CO Carbon monoxide 

CO2 Carbon dioxide 

CVS Constant volume sampling 

DPF Diesel particle filter 

EC Elemental carbon 

EDS Energy-dispersive x-ray spectroscopy 

EPA U.S. Environmental Protection Agency 

FAME fatty acid methyl esters 

g/bhp-hr grams per brake horsepower hour 

NBB National Biodiesel Board 

NOx Oxides of nitrogen 

NREL National Renewable Energy Laboratory 

OC Organic carbon 

ODS Octadecylsilane 

PM Particulate matter 

SOF Soluble organic fraction 

TGA Thermogravimetric analysis 

THC Total hydrocarbon 

ULSD Ultra-low sulfur diesel (petrodiesel having 15 

ppm or less sulfur) 

9
APPENDIX 

Table A-1. Fuel Properties

Property 

Method Units 

2007 Certification 

Diesel 

Neat Soy Biodiesel

(B100) 

Cetane Number D613 41 -- 

Kinematic Viscosity 40C D445 mm2/s 2.211 4.157 

Cloud Point D2500 oC -- 1 

Flash Point D93 oC 78 152 

Total Sulfur D5453 ppm 9 6 

Ash Content D482 wt% <0.001 -- 

Specific Gravity D4052 0.858 -- 

Carbon Residue D524 wt% 0.05 0.04 (neat sample) 

Corrosion, Copper strip D130 1B 1B 

Water and Sediment D2709 vol% 0.01 0.01 

Carbon D5291 wt% 87.27 77.38 

Hydrogen D5291 wt% 13.04 11.86 

Aromatics D1319 %vol 28.2 -- 

Distillation T90 D86 oC 303 -- 

Distillation T90 D1160 oC -- 359.6 

Net Heat of Combustion D240 MJ/kg 42.6 37.3 

Phosphorus D4951 ppm -- <5 

Free Glycerin D6584 wt% -- 0.001 

Total Glycerin D6584 wt% -- 0.236 

Acid Value D664 mg KOH/g -- 0.1 

Sulfated Ash D874 wt% -- <0.001 

10
Table A-2. Heavy-Duty Transient Test Results (commercial ULSD) 

Fuel Run # NOx THC CO PM BSFC 

g/bhp-hr g/bhp-hr g/bhp-hr g/bhp-hr g/bhp-hr 

Without DPF:

2007 Cert 1347 2.09 0.185 1.53 0.1557 189.6 

2007 Cert 1348 2.14 0.271 1.51 0.1434 189.9 

2007 Cert 1349 2.18 0.226 1.56 0.1340 190.7 

2007 Cert 1350 2.18 0.240 1.51 0.1141 190.3 

2007 Cert 1351 2.19 0.247 1.53 0.1293 189.9 

2007 Cert 1354 2.16 0.266 1.52 0.1228 189.7 

2007 Cert 1355 2.17 0.281 1.54 0.1294 189.5 

2007 Cert 1356 2.17 0.257 1.55 0.1345 189.1 

2007 Cert 1357 2.17 0.281 1.51 - 188.8 

Mean 2.16 0.250 1.53 0.1329 189.7 

Standard Deviation 0.03 0.03 0.02 0.01 0.56 

COV% 1.4 12.3 1.2 9.5 0.3 

B20 1359 2.19 0.111 1.23 0.1190 193.5 

B20 1360 2.26 0.137 1.20 0.0918 195.0 

B20 1361 2.28 0.126 1.19 0.0966 195.1 

B20 1362 2.29 0.131 1.18 0.0960 195.4 

Mean 2.26 0.126 1.20 0.1009 194.8 

Standard Deviation 0.04 0.01 0.02 0.01 0.88 

COV% 2.0 9.1 2.0 12.2 0.5 

With DPF:

2007 Cert 1308 2.14 0.002 0.02 0.0017 191.4 

2007 Cert 1309 2.14 0.004 0.03 0.0015 191.7 

2007 Cert 1310 2.13 0.003 0.03 0.0013 190.4 

2007 Cert 1311 2.15 0.001 0.04 0.0012 191.4 

2007 Cert 1336 2.16 0.001 0.02 0.0022 191.8 

2007 Cert 1317 2.16 0.001 0.06 0.0012 191.5 

2007 Cert 1338 2.20 0.004 0.04 0.0012 191.9 

2007 Cert 1339 2.18 0.003 0.06 0.0011 192.2 

2007 Cert 1340 2.19 0.003 0.06 0.0010 191.9 

2007 Cert 1341 2.19 0.003 0.06 0.0011 192.3 

Mean 2.16 0.002 0.04 0.0014 191.6 

Standard Deviation 0.03 0.00 0.02 0.00 0.52 

COV% 1.2 49.2 40.2 27.4 0.3 

B20 1314 2.26 -0.001 0.02 0.0009 194.1 

B20 1315 2.27 0.000 0.03 0.0009 194.7 

B20 1316 2.26 -0.001 0.02 0.0009 192.9 

B20 1328 2.24 0.004 0.02 - 205.8 

B20 1329 2.28 0.000 0.04 0.0010 197.5 

B20 1331 2.25 0.000 0.03 0.0012 196.7 

B20 1332 2.25 0.000 0.03 0.0011 194.1 

B20 1334 2.22 0.000 0.05 0.0009 196.2 

Mean 2.25 0.001 0.03 0.0010 196.5 

Standard Deviation 0.02 0.00 0.01 0.00 4.1 

COV% 0.8 360.0 32.3 10.7 2.1 a

 Negative values indicate emissions below background levels. 

b

 1 g/bhp-h = 1.341 g/kW-h. 

11