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SAE TECHNICAL

PAPER SERIES 2008-01-1401

Effect of Biodiesel (B-20) on Performance

and Emissions in a Single Cylinder

HSDI Diesel Engine

V. Nagaraju and N. Henein

Wayne State University

A. Quader and M. WuDelph

W. BryzikUS TARDEC

Reprinted From: CI Engine Performance for use with Alternative Fuels, 2008(SP-2176)

2008 World CongressDetroit, MichiganApril 14-17, 2008

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ISSN 0148-7191

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ABSTRACT

The focus of this study is to determine the effect

of using B-20 (a blend of 20% soybean methylester biodiesel and 80% ultra low sulfur dieselfuel) on the combustion process, performanceand exhaust emissions in a High Speed DirectInjection (HSDI) diesel engine equipped with acommon rail injection system. The engine wasoperated under simulated turbochargedconditions with 3-bar indicated mean effectivepressure and 1500 rpm engine speed. Theexperiments covered a wide range of injectionpressures and EGR rates. The rate of heatrelease trace has been analyzed in details todetermine the effect of the properties of biodiesel

on auto ignition and combustion processes andtheir impact on engine out emissions. The resultsand the conclusions are supported by a statisticalanalysis of data that provides a quantitativesignificance of the effects of the two fuels onengine out emissions.

LITERATURE REVIEW

In the recent past, researchers have reporteddifferent emission levels of Oxides of Nitrogen

(NOX) from engines fueled with biodiesel B-20.

Biodiesel was found to increase NOX emissions

when compared with regular diesel fuel [1-6].

This increase in NOX has been attributed to

physical properties such as the higher bulkmodules of biodiesel, which would promote anadvance in fuel injection timing and producehigher cycle temperatures, [7-8]. The increase in

NOX was reported to be more prominent in the

pump-line-nozzle and unit injection systems, butwould not appear to be relevant in high-pressurecommon rail injection systems. [4].

However, other researchers have reported that

NOX emissions from biodiesel B-20 are

comparable if not lower than engine outemissions from an engine fueled with regulardiesel fuel [9-12]. This has been attributed to thelower volatility of B-20 compared to regular diesel.

Considering these findings, this work is aimed atexamining the effect of B-20 on the auto ignition,combustion process and engine out emissions ina HSDI diesel engine. Special emphasis is madeon the factors that can cause an increase or drop

in NOX emissions. The tests were conducted at

IMEP=3 bar, engine speed=1500 rpm, andcovered a wide range of injection pressures (P inj),EGR rates, injection timings, injection duration

and a fixed swirl ratio of 3.77(Rs).

EXPERIMENTAL SETUP

The experiments were conducted on a singlecylinder, 4-valve, direct injection, 4 stroke, watercooled, diesel engine equipped with a commonrail fuel injection system capable of delivering fuelpressure up to 1350 bar. The engine wassupercharged with heated shop air. The chargetemperature and pressure in the intake surgetank, in addition to the back pressure in theexhaust surge tank were adjusted to simulateactual turbocharged engine conditions. In theintake manifold, tangential and helical ports werethrottled to different degrees by using gate valvesto attain a swirl ratio of 3.77. An EGR valve wasincorporated which facilitated different EGR levelsof 0, 25, 50, 60 and 64% to be attained. Thedetails of the setup and experimental procedureare given in Ref. [13, 14]. A few differences in thesetup and procedure are described below.

2008-01-1401

Effect of Biodiesel (B-20) on Performance andEmissions in a Single Cylinder HSDI Diesel Engine

V. Nagaraju and N. HeneinWayne State University

A. Quader and M. WuDelphi

W. BryzikUS TARDEC

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The engine has an external water pump forcooling the engine and maintaining it at aconstant temperature for steady state testing, anexternal lube oil pump to provide lubrication andan external fuel delivery system. The abovementioned equipments have been integratedoutside the engine in order to minimize parasiticlosses. The fuel delivery system was designed toavoid changes in the fuel properties due the

instability of biodiesel when exposed toatmospheric air. B-20 was stored in a stainlesssteel fuel tank pressurized with nitrogen gas. Theproperties of B-00 and B-100 are given in Table 4in Appendix C.

Data acquisition was carried out on a Hi-Techniques WIN600 data acquisition system,which measured the cylinder pressure using aKistler 6043A60 water cooled pressuretransducer. The cylinder pressure trace is anaverage of 35 consecutive cycles, and was usedin calculating the average cylinder temperatureand the ARHR (Apparent Rate of Heat Release).Emission measurements were carried out on aHORIBA MEXA 7100 DEGR emissions testbench and a Bosch Smoke Meter was used tomeasure the particulate matter emissions.Emissions data are reported as concentrations,but are equivalent to mass data for comparisonsin this paper since the load was held constant inall the tests.

All results reported in this paper are for Key Point2 (KP2) at an IMEP of 3bar, engine speed of 1500rpm, intake temperature of 150 F (339K) andwith the Location of Peak of Premixed

Combustion (LPPC) of the RHR at 5 after TDC.This assured that the combustion phasing withrespect to TDC was constant and the same for allthe runs reported in this paper. The rest of thetest conditions are given in Appendix B

ANALYSIS OF AUTOIGNITION ANDCOMBUSTION IN A HSDI DIESEL ENGINEFROM ARHR TRACE.

The ARHR trace is divided in seven sections andanalyzed to determine the effect of biodiesel onfuel evaporation, auto ignition and combustion

reactions. Figure 1 shows a typical ARHR traceobtained at IMEP=3bar, Speed=1500 rpm,Injection pressure=1200 bar, EGR=50%, LPPC=5

CAD aTDC and Rs=3.77 for B-20. After fueldelivery at 5.5 CAD bTDC there is a drop in RHRtrace, followed by an increase caused by the coolflame. At this high EGR and injection pressurethe cool flame shows a Negative TemperatureCoefficient (NTC) zone before the start of thepremixed combustion. In this investigation theNTC regime is absent at zero and low EGR rates.

Figure 2 shows the details of ARHR during theearly stages of combustion. The motoredpressure trace (shown in the figure) was obtainedby instantly interrupting fuel injection while theengine was firing and running under constant loadat steady speed. This assured keeping the samewall temperature during motoring and firing. Thedistance from the ARHR of the fired cycle and themotored cycle is the net ARHR. The areas

shown in Figures 1 and 2 can be identified asfollows:

Area 1: Represents the heat transferred from thefresh charge to the liquid fuel for evaporation andthe energy of endothermic reactions.

Area 2: Represents the energy produced fromthe exothermic reactions of the evaporated andpremixed charge mainly in area 1, starting thecool flame.

Area 3: Represents the rest of the energyproduced by the cool flame, before the start of theNTC regime.

Figure 1 - ARHR trace showing the areas thatrepresent the different processes during autoignition and combustion. (Fuel: B-20,

Pinj=1200bar, EGR=50%, Rs=3.77 LPPC=05aTDC)

Figure 2 - ARHR trace showing the details of theareas that represent the auto ignition processesof Figure 1.

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Area 4: Represents the energy released from thecool flame at a lower rate (in the NTC regime)than that in the earlier part of the cool flame.

Area 5: Represents the energy released in thefirst part of the premixed combustion fraction. Itstarts at the end of NTC and ends at the peak ofthe ARHR.

Area 6: Represents the energy released insecond part of the premixed combustion fraction.It starts from the peak of the ARHR to the start ofmixing and diffusion controlled combustionfraction.

Area7: Represents the mixing and diffusioncontrolled combustion fraction. This area startsfrom the end of the premixed combustion fractionto time the exhaust valve opens at 155aTDC.

The effect of B-20 in each of the above areas willbe examined under different operating conditions.Since there were several points in this test matrix,it was difficult to calculate the area under thesedistinct curves manually. A macro program wasdeveloped to run within Microsoft Excel tocalculate these areas. Errors in these areas arecaused by the uncertainties in determining thelocation of the minimum and maximum points inthe ARHR trace. This is particularly the casewhere the trace has a kink or superimposednoise, as shown in Figures 4 and 6. In suchcases, the general trend on the effect of a certainparameter is determined, without considering thepoints that lie out of the trend.

EFFECT OF B-20 ON AUTOIGNITION ANDCOMBUSTION AT DIFFERENT INJECTIONPRESSURES AND EGR RATES

Figure 3 shows a similarity between ARHR tracesfor B-00 and B-20 under this part load conditionwith zero EGR. The amount of fuel injected andthe injection timing for B-20 were slightly changedin order to keep IMEP and LPPC the same asthose for B-00 (as shown in Figure 3). It isnoticed that the auto ignition process occurred inone stage for both fuels under these operatingconditions. But, the peak of ARHR due to

premixed combustion was higher for B-20 than forB-00.

Figure 4 shows the details of the ARHR from SOIto the start of premixed combustion for both B-00and B-20 fuels under the same conditions asemployed in Figure 3. It is noticed that the SOIfor B-20 had to be advanced about 0.25 CAD andthe dialed injection duration increased from 450 to480 sec.

Figure 3 - ARHR for B-20 (solid line) and B-00(dashed line) (IMEP=3 bar, Speed=1500 rpm,

Pinj=600bar, EGR=0% and Rs= 3.77).

Figure 4 ARHR during SOI (details of Figure 3)

Figures 5 and 6 show the ARHR traces for thetwo fuels under a higher injection pressure of1200 bar and higher EGR rate of 60%. The EGR% was calculated from the ratio of CO2 in thefresh charge divided by the total CO2 in theexhaust. It was observed that the SOI wasadvanced for both B-00 and B-20 at 60% EGRand 1200 bar Pinj as compared to the SOI at600bar and 0% EGR to keep LPPC at 5 CADaTDC in both cases. The advance in SOI isbecause of longer ID (Ignition Delay) caused bycharge dilution with EGR, in spite of the increasein mixing at the higher injection pressure. This isdemonstrated for B-00 in Figure 7 at the sameinjection pressure with and without EGR.

It is interesting to notice the SOI for B-00 had tobe more advanced than for B-20, an oppositetrend from 0% EGR. One factor that might havecaused this behavior is the oxygen bound atomsin B-20 and their contribution in the auto ignitionprocess and start of combustion at higher EGR,where the oxygen content of the fresh charge is

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fairly low. In both cases (0 & 60%) the amount ofB-20 injected was higher than B-00. It is clear thatthe two fuels experienced the same pre ignitionprocesses at different injection pressures andEGR rates and showed the NTC regime at highEGR.

Figure 5 - ARHR for B-20 (solid line) and B-00

(dashed line). (IMEP=3 bar, speed=1500 rpm,Pinj=1200bar, EGR=60% and RS=3.77).

Figure 6 - ARHR during SOI (details of Figure 5).

A detailed analysis of the contribution of biodieselcontent of the B-20 blend in the evaporation andendothermic reactions is made by comparingareas 1 and 2 for the two fuels. Figures 8a & 8bgive area 1 for the two fuels at different injectionpressures (600, 800, 1000 and 1200 bar), at twodifferent EGR rates (0% and 50%) and swirl ratioof 3.77. Except for one case (600 bar and 50%EGR) the differences in the areas between thetwo fuels are within the reading errors. Thissuggests that at the swirl ratio of 3.77, the chargethat evaporates, mixes with oxygen, undergoesthe auto ignition reactions and starts combustionis formed from the diesel fuel rather from thebiodiesel content. This can be expected since thediesel fuel is more volatile than the biodiesel. Itshould be mentioned that this finding has beenobserved in other tests conducted under different

injection pressures and EGR rates that are notshown in this paper for brevity.

Figure 7 - ARHR for B-00 [IMEP=3 bar,

Speed=1500 rpm. (Pinj=1200bar, EGR=0% &

60% and RS=3.77)

Figures 8a & 8b - Comparison between heatrelease for B-00 and B-20 during the early stagesof fuel evaporation and endothermic reactions(area 1) at different EGR rates and injectionpressures (IMEP=3 bar, Speed=1500 rpm,variable injection pressure, EGR: 0% & 50%,

RS=3.77)

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Figures 9a & 9b show a comparison betweenarea 2 for B-00 and B-20. Except for onecondition (1000 bar and 50% EGR) area 2 for B-20 is less than or equal to that for B-00. A smallerarea 2 indicates a sharper increase in the rate ofexothermic reactions at the start of the cool flame.This suggests that once auto ignition starts,presumably by the diesel fuel, the rate of theexothermic reactions is enhanced by the biodiesel

component. The oxygen atoms, present in thelighter oil fractions of biodiesel could beresponsible for this sharp increase in exothermicreactions.

Figure 9a & 9b - Comparison between cumulativeheat release during the early stages of cool flame(area 2) for B-00 and B-20, at different EGR rates

and injection pressures. (IMEP=3 bar,Speed=1500 rpm, variable injection pressure,

EGR: 0% & 50%, RS=3.77)

Figures 10a & 10b show the peak of the ARHRdue to the first part of premixed combustionfraction for B-20 to be slightly lower than B-00. Itshould be noted that the amount of B-20 injectedwas more than B-00 to keep IMEP and LPPC thesame for the two fuels. In spite of the more fuelinjected the premixed combustion was less, and

the RHR had a steep rise when compared to B-00. This would suggest that B-20 burnt fastinitially due to the combustion of the lighter oilfraction; however this combustion was notsustained as heavier oil fraction did not evaporateand contribute to the premixed combustion.

Notice the small percentage of C16 (14.8%) for

biodiesel in Table 2 Appendix C.

Figures 10a & 10b - Comparison between peakARHR due to the premixed combustion fraction(Area 5) for B-00 and B-20, at different EGR ratesand injection pressures. (IMEP=3 bar,Speed=1500 rpm, variable injection pressure,

EGR: 0% & 50%, RS=3.77)

Figures 11a & 11b show comparison betweenareas for the late part of premixed combustion(area 6) for B-00 and B-20 at different injectionpressures and at 2 different EGR rates. Except forone point (600 bar and 0% EGR), we notice thatthe area for B-20 is almost equal or larger than forB-00. This supports the idea that the lighterfractions of biodiesel in B-20 burn faster at thestart of combustion and the heavier componentsof biodiesel contribute to the later part of thecombustion process.

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Figure 11a & 11b - Comparison betweencumulative heat release due to the premixedcombustion (areas 6) for B-00 and B-20, at

different EGR rates and injection pressures.(IMEP=3 bar, Speed=1500 rpm, variable injection

pressure, EGR: 0% & 50%, RS=3.77).

Figures 12a & 12b show a comparison betweenarea 7 for mixing and diffusion controlledcombustion for both B-00 and B-20 at 2 differentEGR rates of 0 and 50%. It is observed onaverage, this area is larger for B-20. Thissupports the early discussion for the burning ofthe heavier molecules of biodiesel late in thecycle. This can also be confirmed from Figure 13which shows that for most of the points, theexhaust gas temperatures for B-20 are higherthan for B-00. The statistical analysis (though notcovered in Appendix D) also showed that themean exhaust gas temperature of all the B-20data was slightly higher than for B-00 and thedifference was significant at the 95% confidencelevel.

Figure 12a & 12b Comparison betweencumulative heat releases due to the diffusioncontrolled combustion fraction (area 7) for B-00

and B-20, at different EGR rates and injectionpressures. (IMEP=3 bar, Speed=1500 rpm,variable injection pressure, EGR: 0% & 50%,RS=3.77).

Figure 13 Exhaust gas temperatures for B-00 andB-20 at different injection pressures and EGRrates. (IMEP=3 bar, Speed=1500 rpm, variableinjection pressure, EGR: 0% & 50%, RS=3.77).

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EFFECT OF BIODIESEL IN B-20 ONPERFORMANCE AND EMISSIONS ATVARIOUS EGR RATES AND INJECTIONPRESSURES

OXIDES OF NITROGEN EMISSIONS

Figure 14 shows NOX for B-20 is less than, orequal to that for B-00 under following runningconditions: 3-bar IMEP, 1500-rpm engine speed,and 3.77 swirl ratio. The magnitude of thedecrease was 4% and is significant near the 95%confidence level (Appendix D). The reasoning forthis behavior is not clear at this time because thereaction mechanisms of biodiesel combustion arenot available. But one factor that might havecontributed to this effect is the low volatility of B-20 compared to diesel fuel. The heaviermolecules which are the majority in biodiesel areexpected to be deposited on the walls and burnlate in the cycle, where the gas temperature isdropping during the expansion stroke reducing

NO rate of formation. The late burning of B-20 isevident from the higher exhaust gastemperatures, shown in Figure 13. Also, Figure14 shows that EGR has a much larger impact on

NOX than change in injection pressure as

confirmed by the statistical analysis in AppendixD.

Figure 14 - NOX emissions at different injectionpressures and EGR rates for B-00 and B-20,(IMEP=3 bar, 1500 rpm, variable injection

pressure, EGR: 0%, 25% and 50%, RS=3.77).

CARBON MONOXIDE EMISSIONS

Figures 15 shows that the CO emissions for B-20are lower when compared to B-00 at all EGRrates, particularly at high injection pressures. Themagnitude of this decrease was found to be 3%and was significant at the 95% confidence level(Appendix D). One factor that might have

contributed to this effect, in addition to oxygenatoms in biodiesel molecules, is the betteroxidation reactions during the expansion stroke,where the mass average temperatures are higherwith B-20 than with B-00, as explained earlier. Itshould be noted that the CO oxidation reactionoccurs in a temperature window much lower thanthat for NO formation. Accordingly, the highertemperatures late in the expansion stroke

enhance the oxidation reactions withoutincreasing NOX emissions.

Figure 15 - Carbon Monoxide Emissions for B-00and B-20 at different injection pressures and EGRrates. (IMEP=3 bar, 1500 rpm, variable injection


UNBURNED HYDROCARBONS EMISSIONS

Figure 16 shows that the unburned hydrocarbon

emissions for B-20 are lower than B-00 for allinjection pressures and EGR rates. Themagnitude of the decrease was 9% but was notstatistically significant at the 95% confidencelevels (Appendix D).

Figure 16 Hydrocarbon Emissions for B-00 andB-20 at different injection pressures and EGRrates. (IMEP=3 bar, 1500 rpm, variable injection


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The trend however is similar to that noted inearlier studies Ref [1, 4 &11]. Again this can beexplained by the high hydrocarbon oxidationreaction rates late in the expansion stroke, asexplained earlier. The temperatures achievedduring the combustion of B-20 is higher than B-00only during the later part of the combustionprocess.

SMOKE EMISSIONS

Figure 17 - Bosch Smoke Number for B-00 and B-20 at different injection pressures and EGR rates.(IMEP=3 bar, 1500 rpm, variable injection


Figure 17 shows the Bosch Smoke Number(BSN) for B-00 and B-20. It is difficult to come upwith conclusions from this figure because theleast count of the Bosch Smoke Unit was 0.2;

while the values obtained were low, less than 0.5.The values obtained were interpolated visuallyand hence error bar are drawn with a tolerance of 0.05. The statistical analysis shown in AppendixD confirms this. Though the mean values of allthe Smoke data shows B-20 to be 10% lower thanB-00, this was not significant at the 95%confidence level. In general other studies havereported Smoke to be lower with B-20 relative toB-00 Ref [1, 4, & 11].

INDICATED SPECIFIC FUEL CONSUMPTION

Figure 18 shows ISFC was higher with the B-20as compared to B-00. The magnitude of theincrease was noted to be 7% and statisticallysignificant (Appendix D). This can be attributed totwo factors. The first is the lower heating value ofB-20 compared to B-00 (about 2% lower). Thesecond is the low volatility of biodiesel comparedto the diesel fuel. Upon fuel injection, the volatilecomponents of the fuel evaporate, while theheavier components deposit on the walls. Sincethe wall temperature is much lower than the gastemperature, the rate of evaporation and burning

of the heavier components is slowed downcausing the release of the energy late in theexpansion stroke and a loss in the thermalefficiency. This is evident from the higher exhaustgas temperature with B-20 as compared with B-00, as shown in Figure 13. The reasons for thisincrease are being investigated.

Figure 18 - ISFC for B-00 and B-20 at differentinjection pressures and EGR rates. (IMEP=3 bar,1500 rpm, variable injection pressure, EGR: 0%,

25% and 50%, RS=3.77).

STATISTICAL ANALYSIS OF EMISSIONSAND ENGINE PERFORMANCE DATA

In parallel to the our data analysis based on thephysiochemical combustion model described inthe above section, a statistical analysis tool calledMinitab was used to achieve quantitative analysis

of biodiesel impact on emissions and engineperformance, which are functions of multipleengine operating variables. This statisticalanalysis methodology provides a new avenue toengine data analysis and to help draw definitiveconclusions that are otherwise difficult to quantifyusing the conventional data analysis method.

Minitab is a computer-based analysis tooldesigned to perform statistical functions. It hasthe ability to perform complex statistical analysisof SAS (Statistical Analysis System) and SPSS(Statistical Package for Social Sciences). The

three factors selected for the statistical designwere Fuel, Injection Pressure, and EGR for theprimary matrix. Table 1 shows the number oflevels and their values tested. Appendix D showsthe full factorial design and analysis of the data.The conclusions made in the following section aresupported by a detailed statistical analysis thatquantifies the differences between B-20 and B-00in engine performance and emissions.

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FACTOR LEVELS VALUES

Fuel 2 B-00, B-20

InjectionPressure bar

4600, 800,

1000, 1200

EGR % 4 0, 25, 50, 60

Table 1 Variables and values tested in the first setof designed experiments.

The details of the statistical analysis, the resultson the effect of each parameter on emissions andthe level of confidence are not given in the text forbrevity, and are explained in detail in the

Appendix D.

CONCLUSIONS

The following conclusions are based on anexperimental investigation on a single cylinderHSDI engine using B-00 and B-20 at conditionsthat may be characterized as relatively low speed(1500 rpm), light load (3 bar IMEP), and moderatelevel of swirl (3.77).

EFFECT OF BIODIESEL IN B-20, ON AUTOIGNITION AND COMBUSTION PROCESSES.

1. B-20 did not contribute in the initial stagesof fuel evaporation and the formation ofan ignitable mixture. This has beenvalidated under all the operatingconditions covered in this investigation.There was no statistically significantdifference in start of injection between B-

20 and B-00. B-20 fuel showed a 29%lower ignition delay than B-00 that wassignificant at the 95% confidence level.

2. B-20 enhances the exothermic reactionsleading to the premixed combustion. Thismight be caused by the contribution of theoxygen atom in biodiesel.

3. The peak of the premixed combustionrate of heat release is higher with B-20than B-00 under different operatingconditions. Statistically the maximum rate

of heat release (RHR Max) for B-20 was8% higher than that for B-00.

4. The mixing and diffusion controlledcombustion fractions are higher with B-20than B-00, causing higher exhaust gastemperature for B-20 than B-00.

5. Indicated specific fuel consumption washigher with the B-20 as compared to B-00. Increased fuel consumption with B-20 can be attributed to its lower heating

value and late release of energy in theexpansion stroke.

EFFECT OF BIODIESEL IN B-20, ON ENGINEOUT EMISSIONS.

1. In general NOX has been observed to belower with B-20 than B-00 except at highinjection pressures. Under these

conditions, biodiesel evaporation isenhanced and its contributions in theearly stages of combustion increases andresults in high NOX. Statistically it was

found that B-20 decreased NOX (4%)

relative to B-00 contrary to some previousstudies. Though the effect was small itwas significant near the 95% confidencelevel.

2. In general the incomplete combustionproducts of HC, CO and Soot are lowerfor B-20 than for B-00. This can be the

contribution of the oxygen atom in the fueland the late burning of the heaviercomponents of biodiesel in the expansionstroke. The late burning increases themass average temperature and improvesthe oxidation reactions. Statistically, B-20had no significant effect on smoke andHC emissions. Directionally, B-20decreases smoke and HC (10% lowersmoke and 9% lower HC) relative to B-00. B-20 decreased CO emissions slightly(3%) but this effect was significant at the95% confidence level.

ACKNOWLEDGEMENT

The authors acknowledge the sponsorship of thisprogram by DOE via NextEnergy Center, Detroit,MI under award number DE-FG36-05GO085005.

Also, the technical and financial support of US Army TARDEC, NAC and The AutomotiveResearch Center (ARC) is appreciated. Specialthanks are due to members of the Center for

Automotive Research (CAR) at WSU, particularlyMufaddel Dahodwala for assisting in conductingthe experiments and data analysis, Nathan Sovafor developing the macro program, Lidia

Nedeltcheva and Machine shop. The help andcooperation of Dr. Paul Miles at Sandia NationalLabs are appreciated. Philip Dingle of Delphihelped in the selection of the operating conditionsof the designed experiments.

REFERENCES1. United States Environmental Protection

Agency, A Comprehensive Analysis ofBiodiesel Impacts on Exhaust Emissions;

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EPA 420-P-02-01, EPA: Washington, DC,2002.

2. Tat, M.E. and Van Gerpen, J.H. (2002)Physical Properties and CompositionDetection of Biodiesel-diesel Fuel Blends.

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3. Graboski, M. S.; McCormick, R. L.Combustion of Fat and Vegetable OilDerived Fuel in Diesel Engines. ProgramEnergy Combust. Sci. 1998, 24(2), 125-164.

4. Robert L. McCormick, Christopher J.Tennant, R. Robert Hayes, Stuart Black,John Ireland, Tom McDaniel, AaronWilliams, Mike Frailey Regulated Emissionsfrom Biodiesel Tested in Heavy-DutyEngines Meeting 2004 Emission Standards

SAE Technical Paper No. 2005-01-2200(2005).

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6. A. Senatore and M. Cardone, V. Rocco, M.V. Prati, A Comparative Analysis ofCombustion Process in D. I. Diesel EngineFueled with Biodiesel and Diesel Fuel, SAETechnical Paper No. 2000-01-0691 (2002).

7. Sybist, J.P. and Boehman, A.L. Behavior of A Diesel Injection System with BiodieselFuel SAE Technical Paper No. 2003-01-1039 (2003).

8. Tat, M. E.; Van Gerpen, J. H. Measurementof Biodiesel Speed of Sound and Its Impacton Injection Timing; NREL S/R 510-31462,National Renewable Energy Laboratory:Golden, CO, 2003.

9. C.D. Rakopoulos, K.A. Antonopoulos, D.C.

Rakopoulos, D.T. Hountalas, E.G.Giakoumis, Comparative performance andemissions study of a direct injection Dieselengine using blends of Diesel fuel withvegetable oils or bio-diesels of variousorigins, Renew Energy 0196-8904, 2006Elsevier Ltd.

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and Bioenergy 25 (2003) 309 318 2003Elsevier Ltd.

11. McCormick, A. Williams, J. Ireland, Brimhall,and R.R. Hayes, Effects of Biodiesel Blendson Vehicle Emissions October 2006 FiscalYear 2006 Annual Operating Plan Milestone10.4NREL/MP-540-40554

12. R.L. McCormick, J.R. Alvarez, and M.S.Graboski NOX Solutions for Biodiesel FinalReport 6 in a series of 6, NREL/SR-510-31465

13. N. A. Henein, I.P. Singh, L. Zhong and M-C.Lai, W. Bryzik, New IntegratedO.P.E.R.A.S. Strategies for Low Emissionsin HSDI Diesel Engines SAE TechnicalPaper No. 2003-01-0261(2003).

14. Henein, N. A., Lai, M-C., Singh, I., Wang, D.,and Lui, L., Emission Trade-Off and

Combustion characteristics of a High-SpeedDirect Injection Diesel Engine, SAE paper2001-01-097, SP-1592, 2001.

CONTACT

Question and queries regarding this paper can besent to the authors at:

Vinay Nagaraju, Graduate Research AssistantWayne Sate Universitye-mail: [email protected]

Dr. Naeim Henein, ProfessorWayne State Universitye-mail: [email protected].

Dr. Ather Quader,Delphi Corporatione-mail: [email protected].

Dr. Michael Wu,Delphi Corporatione-mail: [email protected]

APPENDIX A

ABBREVIATIONS

ARHR: Apparent Rate of Heat ReleaseaTDC: After Top Dead CenterbTDC: Before Top Dead CenterB-20: 20% Biodiesel blend with Ultra Low SulfurDiesel FuelB-00: Ultra Low Sulfur Diesel FuelBSN: Bosch Smoke NumberCO: Carbon MonoxideEGR: Exhaust Gas Recalculation

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FA: Fatty AcidsFAME: Fatty Acids Methyl EsterHC: HydrocarbonHSDI: High Speed Direct InjectionIMEP: Indicated Mean Effective PressureID: Ignition DelayISFC: Indicated Specific Fuel ConsumptionLPPC: Location of Peak of PremixedCombustion

NOX: Oxides of NitrogenNTC: Negative Temperature CoefficientPinj: Injection PressurePPC: Peak Pressure in the Cylinderrpm: Revolution Per MinuteRs: Swirl RatioSBO: Soybean OilSFA: Saturated Fatty AcidsSOI: Start of InjectionTDC: Top Dead CenterUFA: Unsaturated Fatty AcidsULSD: Ultra Low Sulfur Diesel Fuel

APPENDIX BTEST CONDITIONS

Intake Pressure: 1.1barExhaust Back Pressure: 1.3bar

Intake Temperature: 1500

F

Coolant Water Temperature: 1800

F

Oil Temperature: 1400

FInjection Pressure: 600, 800, 1000, 1200 barEGR: 0, 25, 50, 60, 62/64 %Swirl Ratio: 3.77Injection Timing: VariableInjection Duration: Variable

IMEP: 3 barSpeed: 1500 rpmFuel 1: B-00 (ULSDF)Fuel 2: B-20 20% blend of Soybean biodieselLPPC: 05 CAD aTDC

APPENDIX C

FUEL PROPERTIES FOR B-100 AND B-00

FAME composition (wt) %

FA SBO

C14:0 0.00%

C16:0 14.10%

C16:1 0.70%

C18:0 5.15%

C18:1 25.29%

C18:2 48.70%

C18:3 6.08%

SFA (%) 19.2

UFA (%) 80.8

Table 2 Soy-derived fatty acid methyl estercomposition (B100)

FEATURE UNITS RESULTS

Distillation-IBP deg F 368

Distillation-5% deg F 403











Recovery % vol. 98.0

Residue % vol. 2.0

Loss % vol. 0

Table 3 Distillation curve for Ultra Low SulfurDiesel Fuel (Distillation cure was obtained fromthe Certificate of Analysis of the manufacturingcompany, Haltermann Products)

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Table 4: Properties of B-00 and B-100

APPENDIX D

STATISTICAL DATA ANALYSIS

Table D-1 shows the full matrix of 32 test pointsand some of the responses. The analysis ofvariance (ANOVA) for main effects and two factor

interactions for the NOX emissions data areshown in Table D2 (output from Minitab). ANOVAis a statistical method for evaluating the differenceamong means. Values of P (last column headerin Table D2) less than 0.05 indicate factors thathave a significant impact at 95% confidence level

on the NOX response. Other column headers in

Table D2 are the output from Minitab representing

intermediate statistical terms, though important tostatisticians, but are neither a focus of this paper,nor discussed here. EGR with a P value of 0.000is clearly identified as a significant main effect.Fuel with a P value of 0.051 not exactly significantat the 95% confidence level however it is veryclose. None of the other factors (source terms)are significant at the 95% confidence level.

The main effect plots for the NOX response are

shown in Figure. D1. The mean value of all the

NOX data for the B-00 fuel was 374 ppm, whilethe mean value with the B-20 fuel was 358.1 ppm.

Thus the 4% lower mean NOX emission with the

B-20 relative to B-00 data in this matrix wasnumerically small however the difference wasstatistically significant at the 94.9% confidencelevel. The lower NOX emission with B-20 relative

to B-00 is contrary to the trend of higher NOX with

B-20 reported in the literature. The statistics onlyindicates whether or not the difference isstatistically significant however it does notindicate the reason for this behavior. Theknowledge of the factors that increase or

decrease the NOX emissions during the

combustion process gives a good indication as tothis behavior. For instance changes in ignitiondelay and/or rate of heat release with B-20 could

contribute to the slightly lower NOX emissions

relative to B-00. However the ignition delay andrate of heat release data should be analyzed todetermine this for certain, this analysis is shownin the following sections. Moreover, the manner

in which the engine was run in these tests mayalso contribute to lower NOX with B-00. Thecrank angle for maximum rate of heat release wasadjusted so that it occurred at 5 degrees afterTDC during each test by controlling the fuelinjection timing. This results in similar phasing ofcombustion around TDC for both B-20 and B-00.This may also contribute to similar or slightly

lower NOX emissions with B-20 as noted above.

The impact of EGR (dilution) on NOX emissions is

well known. EGR is known to decrease themaximum combustion temperature that leads to

lower NOX emissions. This is clearlydemonstrated by the large decrease (99%

decrease) in NOX with EGR (from 0% to 60%EGR) and the high confidence level associatedwith the statistical analysis. The decrease (96%)is linear up to 50% EGR and little effect of EGRbeyond 50%. Injection pressure had no

significant impact on NOX emissions in this data

set.

The ANOVA results in Table D2 showed nosignificant effect of two factor interaction terms.

Hence plots of two factor interaction terms are notshown.

The ANOVA of the smoke response similar toTable D2 was obtained from the statisticalanalysis however it is not shown in this section forbrevity. Injection pressure and EGR aresignificant main effects at the 95% confidencelevel according to the ANOVA for smoke data.The interaction term Injection pressure*EGR, isalso significant in this data. The main effect plotsfor smoke are shown in Figure.D2 and theinteraction plots are shown in Figure.D3.

In Figure.D2, smoke decreased slightly (-10%)with B-20 relative to B-00, similar trend to earlierstudies. The difference however, is notstatistically significant at the 95% confidencelevel. Among other main effects in Figure.D2,smoke decreased significantly (54%) with higherinjection pressure. The decrease is near linearwith injection pressure increase from 600 bar to1200 bar. This is perhaps due to smaller drop sizeand better mixing of fuel with air at higherinjection pressures. Smoke variation was

PROPERTYTESTINGMETHOD

B-00 B-100

Flash Point (C) ASTM D93 178 157

Viscosity 400C

(mm2/sec)

ASTMD445

2.4 4.317

SulfurASTMD5453

10ppm

0.0004% mass

Cetane Number ASTMD613

40.9 47.5

Cloud point (C) D 2500 3 -25

Pour point (C) D 97 -3 -36

Cold filter pluggingpoint (C)

D 6371 -3 -26

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somewhat inconsistent with EGR but in generalshows a trend to increase with EGR as expected,and is statistically significant. The highest smokeemission at 60% EGR was 35% higher than thatat no EGR.

In Figure.D3, the interaction between the injectionpressure and EGR was the only two factorinteraction that was significant. At no EGR smoke

emissions showed a smaller decrease withincreased injection pressure, while at 60% EGRlarger decrease in smoke with higher injectionpressure is indicated. Again the statisticalanalysis indicates that this effect is significant atthe 95% confidence level but the underlyingreason is not clear. Fuel interactions with otherfactors were not statistically significant but at 600bar injection pressure and 0% EGR B-20displayed lower smoke emissions than B-00 inFigure.D3.

The HC response according to the ANOVA (notshown) was quite similar to the smoke responsein that fuel effect on the HC emission was notsignificant at the 95% confidence level. As withthe Smoke response the main effects of injectionpressure and EGR and the interaction terminjection pressure*EGR were significant at the95% confidence level according to the ANOVA forthe HC emission response (not shown here).Figure.D4 shows the main effect plots for HCwhile Figure.D5 shows the two factor interactionplots. In Figure.D4 HC emissions were slightlylower (-9%) with B-20 relative to B-00 but notstatistically significant at these very low overallHC levels. This point requires data at higher

loads where HC should be higher and easier toidentify the differences.

HC emissions increased significantly (+30%) withhigher injection pressure (from 600 to 1200 bar) inFigure.D4. Perhaps higher injection pressurecauses more penetration of the fuel and possibleover mixing resulting in lack of burning and higherHC. Also shown in Figure.D4, HC emissionsincreased significantly with EGR as expected(almost 5.5 times higher at 60% EGR relative tono EGR).

The two-factor interaction between injectionpressure and EGR is significant in Figure.D5. Atno EGR there was no effect of injection pressure,while at 60% EGR HC increased with higherinjection pressure. The reason for this behavior isnot clear, however it could be speculated that athigh EGR levels increasing the injection pressurehas an adverse effect of increased fuelpenetration and over mixing of the fuel/air/EGRmixture, rendering some parts of the charge noncombustible (beyond the lean flammability limit).For CO emissions all three main effects (Fuel,

Injection Pressure and EGR) were significant atthe 95% confidence level according to the

ANOVA for the CO emissions results (not shown).Moreover, the two factor interaction term InjectionPressure*EGR was also significant.

Figure.D6 shows the main effect plots of the COemissions while Figure.D7 shows the interactionplots of the CO emissions. The main effect trends

for CO in Figure.D6 were quite similar to thetrends for HC shown in Figure.D4. CO emissionswere 3% lower with B-20 fuel compared with B-00, but the effect was significant at the 95%confidence level. The CO emissions increased29% with injection pressure increase from 600 to1200 bar in Figure.D6. EGR caused largeincreases in CO emissions. The magnitude of theincrease was 20 fold from 0% EGR to 60% EGRin Figure.D6, with most of the increase occurringbetween 50% -60% EGR.

The significant two-factor interaction betweeninjection pressure and EGR is shown inFigure.D7. With no EGR there was little or noeffect of injection pressure, while at 50% EGR COincreased with injection pressure. With 60% EGRthe CO values were pegged at the max of therange (5200 ppm) for injection pressures above800 bar. This is evident in the engine out COemission data values in Table D1 for run ordernumbers 8, 12, 16, 24, 28, and 32. Pegging of theCO data at high EGR levels, impacts the datameans which are underestimated and increasesthe error estimates. Inserting extrapolatedestimates in place of the pegged values loweredthe error estimates. Hence the reported

confidence levels with the pegged values in thedata set are conservative.

Indicated specific fuel consumption (ISFC), startof injection (SOI), ignition delay (ID0), andmaximum rate of heat release (ROHR Max) dataof the designed tests are analyzed next. All maineffects had a statistically significant impact onISFC according to the ANOVA of the ISFC results(not shown). None of the two factor interactionswere significant at the 95% confidence level.

Figure.D8 shows the main effect plots for theISFC data. ISFC increased significantly (+7%)with B-20 relative to B-00. Biodiesel (B100) hasless energy per unit mass so higher fuelconsumption is expected but the magnitude ofincrease for B-20 appears too high. ISFC alsoincreased significantly (+13%) with injectionpressure from 600 to 1200bar. The increase inISFC with higher injection pressure may becaused by greater penetration and over mixingresulting in incombustible mixture in the peripheryof the spray. Note that HC and CO were also

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increased with injection pressure for similarreason pointed out earlier. The ISFC decreased3.4% with increasing EGR from 0% to 50%,before increasing (+4.9%) from 50% to 60% EGRin Figure.D8. This may be due to EGR favorablyimpacting the ratio of specific heats (by loweringthe temperature) of the working fluid up to a pointbefore further increase in EGR adversely slowsdown combustion and increases ISFC.

Fuel and injection pressure had no significantimpact on the SOI. EGR however had asignificant impact on SOI. The interactionbetween injection pressure and EGR wassignificant. These statements are based on the

ANOVA of the start of injection timing (SOI) notshown here.

The main effect plots for SOI are shown in Figure.D9 and the interaction plots are shown in Figure.D10. In Figure.D9 there was no significantdifference in SOI between B-20 and B-00. Thusthe start of injection timing was essentiallyunchanged between B-00 and B-20. Also therewas no significant impact of injection pressure inSOI. Increasing EGR moved the SOI to earlier(more advanced) values particularly at high EGRlevels. This is due to slower burn rate at higherEGR.

In Figure.D10 the interaction of injection pressurewith EGR was significant. At 0% EGR increasinginjection pressure moved SOI closer to TDC(slight retard) implying faster burning, but with60% EGR increasing injection pressure advancedSOI slightly indicating slower burning.

The ANOVA of ignition delay (not shown)indicates that Fuel and EGR are significant maineffects and the interaction between Fuel and EGRis also significant.

Figure.D11 shows the main effects plots ofignition delay, while Figure.D12 shows theinteraction plots. In Figure.D11 B-20 fuel has a29% lower ignition delay than B-00. Other studieshave also shown shorter ignition delay withbiodiesel fuels. The shorter ignition delay with B-20 will result in less time for vaporization and

therefore less premixed burning that could resultin lower NOX emissions in the initial combustionphase with B-20 relative to B-00. This could be afactor contributing to lower NOX emissions with B-20 noted in Figure.D1. In Figure.D11 increasingEGR from 0% to 60% is seen to double theignition delay. This is the well known dilutioneffect of EGR slowing down the pre-flamereaction during the induction period andincreasing the ignition delay. The interaction plotsof fuel and EGR in Figure.D12 shows that at 60%EGR the B-00 fuel increases the ignition delay

much more than the B-20 fuel. This could be dueto rapid degradation of combustion with B-00 at60% EGR. The implication is that B-20 has betterEGR tolerance than B-00.

The ANOVA for the maximum Rate of HeatRelease (RHR Max) shows that all three maineffects were significant at the 95% confidencelevel for RHR Max. The interaction between

injection pressure and EGR was also significant.Figure.D13 and Figure.D14 show the main effectand interaction plots respectively for RHR Max.The RHR Max for B-20 was 8% higher than thatfor B-00. This implies faster burning of the chargewith B-20. In general faster burning is associatedwith higher combustion temperature and shouldcontribute to higher NOX emissions with B-20.The opposing effect of shorter ignition delay andless premixed combustion and lower NOXsuggests that in these tests the factors thatcontribute to lower NOX dominate the factors thatincrease NOX. The net effect of these opposingeffects seems to lead to lower NOX with B-20 inthese tests.

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Table D1 Full factorial design test points with emission and ISFC responses

Analysis of Variance for NOx ppm, using Adjusted SS for Tests

Source DF Seq SS Adj SS Adj MS F P

Fuel 1 1845 1845 1845 5.06 0.051

Inj Pressure bar 3 2398 2398 799 2.19 0.159

EGR % 3 4706675 4706675 1568892 4298.95 0.000

Fuel*Inj Pressure bar 3 39 39 13 0.04 0.990

Fuel*EGR % 3 840 840 280 0.77 0.540

Inj Pressure bar*EGR % 9 1960 1960 218 0.60 0.773Error 9 3285 3285 365

Total 31 4717042

S = 19.1036 R-Sq = 99.93% R-Sq(adj) = 99.76%Table D2 Analysis of variance for NOx emissions. Column headers DF, Seq SS, Adj SS, Adj MS , F, and Pare statistical terms from Minitab output.

M INITAB DO E (design of experiment) Base M atrixStdO rder F ue l Inj Pressur EG R C O ppm H C ppm N Ox ppm Sm oke BS ISF C g/kw -

1 B0 600 0% 185 90 975 0.26 222.428

2 B0 600 25% 297 113 504 0.228 225.055

3 B0 600 50% 1417 220 54 0.3 217.193

4 B0 600 60% 4639 480 12 0.3875 233.668

5 B0 800 0% 222 100 953 0.25 231.304

6 B0 800 25% 374 121 462 0.26 227.081

7 B0 800 50% 1932 263 39 0.141 227.988

8 B0 800 60% 5200 577 13 0.265 240.879

9 B0 1000 0% 269 99 978 0.164 233.008

10 B0 1000 25% 803 170 446 0.1833 242.555

11 B0 1000 50% 2456 313 37 0.14 238.598

12 B0 1000 60% 5200 615 14 0.135 239.55

13 B0 1200 0% 367 107 971 0.125 236.936

14 B0 1200 25% 623 152 473 0.138 236.31

15 B0 1200 50% 2457 322 39 0.0933 237.991

16 B0 1200 60% 5200 731 14 0.1125 244.457

17 B20 600 0% 192 89 996 0.125 238.107

18 B20 600 25% 337 148 453 0.2 234.995

19 B20 600 50% 1450 185 38 0.22 230.877

20 B20 600 60% 4622 401 10 0.34 235.781

21 B20 800 0% 202 80 914 0.166 249.93622 B20 800 25% 366 107 440 0.15 242.048

23 B20 800 50% 1871 204 36 0.175 238.901

24 B20 800 60% 5200 520 9 0.3 250.812

25 B20 1000 0% 215 84 904 0.1833 254.979

26 B20 1000 25% 696 147 456 0.26 256.726

27 B20 1000 50% 2104 225 36 0.14 233.993

28 B20 1000 60% 5200 714 9 0.158 261.615

29 B20 1200 0% 247 89 945 0.1142 284.975

30 B20 1200 25% 525 129 455 0.15 251.301

31 B20 1200 50% 2280 233 33 0.1 259.662

32 B20 1200 60% 5200 715 7 0.13 271.674

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Meanof

RHRMax(J/CAD)

B20B0

150

125

100

75

50

12001000800600

6050250

150

125

100

75

50

Fuel InjectionPressurebar

%EGR

MainEffectsPlot (datameans)forRHRMax (J/CAD)

Significant Effect

Significant Effect Significant Effect+8% +13%

-69%Meanof

RHRMax(J/CAD)

B20B0

150

125

100

75

50

12001000800600

6050250

150

125

100

75

50

Fuel InjectionPressurebar

%EGR

MainEffectsPlot (datameans)forRHRMax (J/CAD)

Significant Effect


-69%

Significant Effect


-69%

Figure D13 Main effect plots of RHR Max Figure D14 Interaction plots of RHR Max

Fuel

150

100

50

12001000800600

Injection Pressurebar

150

100

50

B20B0

150

100

50

%EGR

6050250

B0

B20

Fuel

600

800

1000

1200

bar

Pressure

Injection

0

25

50

60

%EGR

InteractionPlot (datameans)forRHRMax (J/CAD)

Significant

Significant

Documents

2008-01-1401