li --.-A Lean-Burn Characteristics of a Gasoline Engine Enriched with Hydrogen from a Plasmatron Fuel Reformer By

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1 - Lean-Burn Characterstcs of a Gasolne Engne Enrched wth Hydrogen from a Plasmatron Fuel Reformer By Edward J. Tully B.S., Chemcal Engneerng Case Western Reserve Unversty, 1997 Submtted to the Department of Mechancal Engneerng n Partal Fulfllment of the Requrements for the Degree of Master of Scence n Mechancal Engneerng at the Massachusetts nsttute of Technology June 2002 BE,RKER MASSACH USETTS NSTTUTE OFTECHNOLOGY 2002 Massachusetts nsttute of Technology All Rghts Reserved OCT LBRARES -- Sgnature of Author Certfed by Department of Mechancal neerng Juf 10, 2002 Al-L- /3 l --.-A John B. Heywood Sun Jae Professor of Mechancal Engneerng Thess Advsor Accepted By ~~~3~~~~~m;~~~~ An A. Sonn Professor, Department of Mechancal Engneerng Charman, Department Graduate Commttee

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3 Lean-Burn Characterstcs of a Gasolne Engne Enrched wth Hydrogen from a Plasmatron Fuel Reformer By Edward J. Tully Submtted to the Department of Mechancal Engneerng June 2002 n Partal Fulfllment of the Requrements for the Degree of Master of Scence n Mechancal Engneerng ABSTRACT f a small amount of hydrogen s added to a gasolne fueled spark gnton engne the lean lmt of the engne can be extended. Lean runnng engnes are nherently more effcent. and have the potental for sgnfcantly lower NOx emssons. Hydrogen addton reduces the combuston varablty. n ths engne concept supplemental hydrogen s generated on-board the vehcle by dvertng a small fracton of the gasolne to a plasmatron where t s partally oxdzed nto a stream contanng hydrogen, carbon monoxde, ntrogen. and carbon doxde. t s then mxed n the ntake port wth the man fuel/ar charge to provde hydrogen enhanced lean operaton A seres of experments were performed to study the feasblty of ths engne concept. Snce the plasmatron s stll under development the fnal composton of the plasmatron gas s not yet known. Therefore, two dfferent bottled gases were used to smulate the plasmatron output. An deal plasmatron gas (H 2, CO, and N 2 ) was used to represent the output of the theoretcally best plasmatron. n addton, a typcal plasmatron gas (H,. CO. N 2, and CO2) was used to represent the current output of the plasmatron. n addton, a seres of hydrogen only addton experments were performed to quantfy the mpact of the non-hydrogen components n the plasmatron gas. Varous amounts of plasmatron gas were used, rangng from the equvalent of 10%-30% of the gasolne beng converted n the plasmatron. At each of these fractons a sweep of. the relatve ar/fuel rato was performed, startng at stochometc and slowly ncreasng lambda untl the engne began to msfre. At each operatng pont data was collected to quantfy effcency, emssons, and combuston stablty. All of the data was compared to a baselne case of the engne operatng stochometrcally on gasolne only. t was found that the peak net ndcated fuel converson effcency of the system ncreased 12% over the baselne case. n addton, at ths peak effcency pont the engne out NOx emssons decrease by 94% (165ppm vs. 2800ppm) whle the hydrocarbon emssons decreased by 6% (2210ppm vs. 2350ppm). NOx emssons reductons of 99% were possble although they occured at slghtly lower overall effcency ponts. 3

4 n the analyss the relatve ar/fuel rato was found to be an nadequate measure of mxture dluton. Two new dluton parameters were defned. The Volumetrc Dluton Parameter, VDP, represents the heatng value per unt volume of the ar/fuel mxture. Pumpng work reductons due to dluton correlate wth VDP. The Thermal Dluton Parameter, TDP, represents the heatng value per unt heat capacty of the fuel/ar mxture. Combuston and emssons parameters correlate wth TDP. 4

5 ACKNOWLEDGEMENTS The end. At tmes thought ths day would never come. Sxteen months ago become a member of the Sloan Automotve Lab. Snce then have felt exctement, frustraton, surprse, falure, and ultmately success. Throughout the entre process have had the support of many people that have made my experence at MT nvaluable. Wthout them none of ths would have been possble. Frst would lke to thank Professor John Heywood for beng my thess advsor. Professor Heywood encouraged me every step of the way, provdng drecton when necessary but also gvng me the freedom to contrbute my own deas to the research project. Hs contnuous support has greatly enhanced my tme spent at MT. n addton would lke to thank Professor Wa K. Cheng. Professor Cheng provded creatve solutons for dealng wth equpment problems that caused havoc wth my data collecton. Wthout hs help would probably stll be standng n my test cell, pullng my har out n frustraton. Grant number DE-AC03-99EE50565 from the US Department of Energy supported ths work. would lke to thank the Dr. Rogelo Sullvan and Sdney Damond of the US Department of Energy for ths support. The assstance n the lab has been excellent. Thane Dewtt helped wth all types of techncal ssues whle Alexs Rozantes provded solutons to my admnstratve questons. n addton, Karla Stryker always somehow managed to squeeze me nto Professor Heywood's busy schedule. Wthout ths group my research would have been much more dffcult to complete. Every sngle student n the Sloan Auto Lab has had a postve mpact on my stay at MT. Several have done a tremendous amount to help me along the way. Andreas Lengwler preceded me on the plasmatron project and helped n settng up much of the necessary expermental hardware. Jenny Topnka worked closely wth me for the past academc year and performed many hours of analyss and smulaton n support of ths project. Addtonally, Bran Hallgren helped n many ways from equpment setup to data analyss, not to menton the many hours of laughter he provded. Many more reman unnamed but are no less mportant. Fnally would lke to thank my employer, General Motors. Ther backng has been substantal and they have gone out of ther way to provde both fnancal and admnstratve support. Wthout ther assstance would not have had ths ncredble opportunty. 5

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7 TABLE OF CONTENTS Abstract Acknowledgements Table of Contents... 7 Lst of Fgures Chapter 1: ntroducton and Background : Current State of Gasolne S and Desel Engnes : Supplemental Hydrogen Addton Concept : Plasmatron Engne Concept l 3 1.4: Plasmatron Operaton Chapter 2: Engne Setup and Data Acquston : Engne Setup : Engne Control : Fuel Data : Data Acquston : Test Setup : Arflow Measurement : ndolene Flow Rate Control... 19') 2.4.4: Plasmatron Flow Rate Control : Lambda Measurement : n-cylnder Pressure Measurement : Hydrocarbon Emssons Measurement : NOx Emssons Measurement : Data Analyss Software Chapter 3: Expermental Structure : ncreasng Bum Rate '3 3.2: Plasmatron and Hydrogen Addton Experments : Expermental Procedure : Equvalent Percent Plasmatron Defnton : Dluton Parameters Chapter 4: Results and Dscusson : Error Analyss : MBT Tmng : Burn Duraton : Combuston Stablty : Hydrocarbon Combuston Effcency : NOx Emssons : Fuel Converson Effcency : Engne Only Fuel Converson Effcency : Overall System Fuel Converson Effcency Chapter 5: Conclusons References Appendx

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9 LST OF FGURES Fgure Flame Speed and Dluton Lmt Data for Selected Compounds Fgure Plasmatron Engne Concept Fgure Schematc of a Plasmaton Fuel Reformer Fgure deal and Typcal Plasmatron Composton and Effcency Fgure Basc Engne Data Fgure Selected Fuel Propertes Fgure Schematc of the Expermental Setup... 8 Fgure ntake Plate Desgns Fgure MBT Spark Tmng vs. Lambda for Dfferent ntake Plates Desgns Fgure Plasmatron Engne Schematc: Arflow and Fuel Flow Fgure Expermental Setup for Plasmatron and Hydrogen Addton Fgure Energy Balance on System Usng a Plasmatron Fgure 3.6-0%-10% Burn Angles vs. Lambda - deal Plasmatron and Hydrogen Addton Fgure 3.7-0%-10% Burn Angles vs. VDP - deal Plasmatron and Hydrogen Addton Fgure 3.8-0%-10% Burn Angles vs. TDP for deal Plasmatron and Hydrogen Addton Fgure Calculated Lambda vs. UEGO Lambda Fgure Absolute Error n Lambda vs. UEGO Lambda Fgure MBT Spark Tmng vs. Lambda - Typcal and deal Plasmatron Addton Fgure MBT Spark Tmng vs. TDP - Typcal and deal Plasmatron Addton Fgure MBT Spark Tmng vs. Lambda - deal Plasmatron and Hydrogen Addton Fgure MBT Spark Tmng vs. TDP - deal Plasmatron and Hydrogen Addton Fgure 4.7-0%-10% Burn Duraton Angle vs. Lambda - Typcal and deal Plasmatron Addton Fgure 4.8-0%-10% Burn Duraton Angle vs. TDP - Typcal and deal Plasmatron Addton Fgure %-90% Burn Duraton Angle vs. Lambda - Typcal Plasmatron and deal Plasmatron Fgure %-90% Burn Duraton Angle vs. TDP - Typcal Plasmatron and deal Plasmatron Fgure %-90% Bum Duraton Angle vs. Lambda - deal Plasmatron and Hydrogen Addton Fgure %-90% Burn Duraton Angle vs. TDP - deal Plasmatron and Hydrogen Addton Fgure COV of MEP vs. Lambda - Typcal Plasmatron and deal Plasmatron Fgure COV of MEP vs. TDP - Typcal Plasmatron and deal Plasmatron Fgure COV of MEP vs. Lambda - deal Plasmatron and Hydrogen Addton...61 Fgure COV of MEP vs. TDP - deal Plasmatron and Hydrogen Addton

10 Fgure Percent Unburned Hydrocarbons vs. Lambda - Typcal and deal Plasmatron Fgure Percent Unburned Hydrocarbons vs. TDP - Typcal and deal Plasmatron Fgure Percent Unburned Hydrocarbons vs. Lambda - deal Plasmatron and Hydrogen Addton Fgure Percent Unburned Hydrocarbons vs. TDP - deal Plasmatron And Hydrogen Addton Fgure NOx emssons vs. Lambda - Typcal and deal Plasmatron Fgure Log Scale of NOx emssons vs. Lambda - Typcal and deal Plasm atron Fgure NOx emssons vs. TDP - Typcal and deal Plasmatron Fgure Log Scale of NOx emssons vs. TDP - Typcal and deal Plasmatron...65 Fgure NOx emssons vs. Lambda - deal Plasmatron and Hydrogen Addton Fgure Log Scale of NOx emssons vs. Lambda - deal Plasmatron and Hydrogen Addton Fgure NOx emssons vs. TDP - deal Plasmatron and Hydrogen Addton Fgure Log Scale of NOx emssons vs. TDP - deal Plasmatron and Hydrogen Addton Fgure Engne only Fuel Converson Effcency vs. Lambda - Typcal and deal Plasmatron Fgure Engne only Fuel Converson Effcency vs. VDP - Typcal and deal Plasmatron Fgure Engne only Fuel Converson Effcency vs. Lambda - deal Plasmatron and Hydrogen Fgure Engne only Fuel Converson Effcency vs. VDP - deal Plasmatron and Hydrogen Fgure Overall Fuel Converson Effcency vs. Lambda - Typcal and deal Plasmatron Fgure Overall Fuel Converson Effcency vs. VDP - Typcal and deal Plasm atron Fgure Overall Fuel Converson Effcency vs. Lambda - deal Plasmatron and Hydrogen Addton Fgure Overall Fuel Converson Effcency vs. VDP - deal Plasmatron and Hydrogen Addton Fgure Overall Net ndcated Fuel Converson Effcency vs. Relatve NOx emssons - All Data Fgure Overall Net ndcated Fuel Converson Effcency vs. COV - All Data

11 Chapter 1: - ntroducton and Background Current State of Gasolne Spark gnton and Desel Engnes Currently the two domnant engne technologes n the automotve ndustry are the desel engne and the gasolne spark gnton (S) engne operatng stochometrcallv. A promsng thrd engne technology s the hydrogen enrched lean operatng gasolne sparkl gnton engne. Because desel engnes are desgned to operate globally lean the throttle can be elmnated whch sgnfcantly reduces pumpng losses. n addton. the desel engne can operate at a sgnfcantly hgher compresson rato then the stochometrcally operated spark gnton engne, whch provdes an addtonal effcency beneft. Globally the desel engne operates lean of stochometrc although the ar/fuel mxture nsde the cylnder s not homogeneous. Locally, the charge can be fuel rch, stochometrc. or lean. Combuston that occurs near stochometrc results n hgh flame temperatures. whch drves ntrc oxde (NO) formaton. n addton, the combuston that occurs n the fuel rch regon s less complete and results n soot formaton. An addtonal problem s that desel exhaust s very dffcult to treat. The exhaust gas s a hghly oxdzng envronment whch makes the reducton of ntrogen oxdes (NOx) to ntrogen and oxvygen an especally challengng problem. Most desel engnes are currently sold wthout aftertreatment systems nstalled, resultng n hgh talppe out emssons of NOx and partculates. The gasolne engne typcally operates wth a charge that s both homogeneous and stochometrc. The man benefts to operatng stochometrcally are that a hghlv effcent three-way catalyst can be used. and the turbulent premxed flame combuston process s fast. Although the engne out NOx emssons are relatvely hgh due to the hgh burnt gas temperatures, the use of exhaust gas recrculaton (EGR) and a hghly effcent three-way catalyst results n very low talppe emssons. The man drawback s that the engne must be throttled at part load. resultng n sgnfcant pumpng losses. n addton, the knock lmts are lowest near stochometrc operaton. necesstatng lower compresson ratos. 11

12 1.2 - Supplemental Hydrogen Addton Concept An alternatve engne concept s the gasolne engne whch operates both lean and wth a homogeneous ar/fuel mxture. Studes have shown that the addton of a small amount of hydrogen can cgreatly ncrease the lean lmt of the engne [1]. By operatng wth excess ar the engne s nherently more effcent and s less throttled, whch greatly reduces the pumpng losses and further ncreases effcency. By operatng wth a homogeneous lean charge the peak combuston temperatures are much lower than n desel or S engnes, resultng n much lower engne-out NOx emssons. At very lean condtons the NOx emssons may be low enough to elmnate aftertreatment. The largest obstacle to overcome wth ths concept s n achevng fast and stable combuston at very lean condtons. As excess ar s added the flame speed slows, causng burn duratons and combuston varablty to ncrease. Eventually, the mxture becomes so dlute that t wll no longer support stable combuston. Gasolne has a relatvely low dluton lmt wth combuston deteroratng rapdly as excess ar s added. One soluton s to add a small amount of a fuel that has much faster combuston characterstcs. Hydrogen (H 2 ) s an excellent canddate because t has a much hgher dluton lmt and flame speed than typcal hydrocarbons [2]. Lamnar Flame Speed (cm/sec) Lean Lmt n Ar Stochometrc Maxmum Relatve AFR (Lambda) Hydrogen Carbon Monoxde Benzene Propane Fgure Flame Speed and Dluton Lmt Data for Selected Compounds Benzene and propane were chosen as representatve straght chaned and cyclc hydrocarbons. Although ndolene s a mxture of many dfferent hydrocarbons most of them have very smlar burn propertes to benzene and propane. The carbon monoxde (CO) data s ncluded because t s present n the plasmatron engne concept. whch s NOTE: Fgures showng expermental data are presented at the end of each chapter. contaned wthn the body of the paper. All other t"gulrcs arc 12

13 dcussed n the next secton. Although hydrogen has some very good combuston characterstcs t s not wdely used as a fuel for several reasons. Frst, hydrogen s a gas at room temperature and therefore must be stored n hgh pressure tanks on the vehcle whch poses sgnfcant safety rsks. n addton, there s no nfrastructure avalable to dstrbute hydrogen and the constructon of one would be expensve. Fnally, hydrogen s not wdely avalable n nature and f large quanttes were needed t would have to be made from ether the electrolyss or water or from the partal oxdaton of a hydrocarbon. For these reasons t s unlkely that hydrogen wll be wdely avalable as a vehcle fuel source Plasmatron Engne Concept One alternatve to storng hydrogen on the vehcle s to generate hydrogen on board the vehcle usng a partal oxdaton fuel reformer. Several studes have shown that the use of an on-board fuel reformer can sgnfcantly reduce emssons and potentally ncrease effcency [3,4]. n ths concept gasolne and ar enter the reformer and the fuel s partally oxdzed to form a stream that conssts prmarly of hydrogen. carbon monoxde. and ntrogen. Plasmatron Engne Concept A: _ Fgure Plasmatron Engne Concept 13

14 The process s exothermc, wth approxmately 15%-20% of the chemcal energy of the ndolene beng converted to waste heat durng the converson process. Ths hydrogen rch stream s then combned wth the ndolene and ar to form a homogeneous mxture pror to combuston. Due to the losses n the reformer the fracton of the fuel that s reformed should be mnmzed. A seres of experments were performed to nvestgate ths engne concept. Because the plasmatron s stll n development, bottled gases were used to smulate the plasmatron output gas. Three dfferent reformed fractons of fuel were nvestgated: 10%. 20%. and 30%. The reformed fracton s defned as the fracton of the gasolne that s sent through the plasmatron. Two dfferent mxes of bottled gases were used, one representng the current output of a prototype plasmatron desgn, and one representng a best case or deal plasmatron. n addton, whle t s known that hydrogen addton wll ncrease the lean combuston lmts of the engne, t was unclear as to the mpact of the ntrogen (N 2 ) and CO n the plasmatron gas. To assess ths, experments were performed wth straght hydrogen addton. n total there were 3 fuels, each wth 3 dfferent reformed factons. plus the baselne case of gasolne only for a total of 10 dfferent fuelng combnatons. Comparsons between the typcal and deal plasmatron gas at a fxed reformed fracton could show the potental beneft of mprovng the actual plasmatron. Comparsons between the deal plasmatron and hydrogen addton could assess the mpact of the other components n the plasmatron gas. Fnally, all of these cases were compared to a baselne case of the engne run on ndolene only. All of the experments were performed at a fxed load and speed on a modfed Rcardo sngle-cylnder research engne. For each case a sweep of the relatve ar/fuel rato (lambda) was performed, startng at stochometrc and steppng lambda untl the engne began to msfre. Lambda at the msfre lmt vared from 1.8 to 2.1 dependng on the fuel. At each pont the followng measurements were taken: n-cylnder pressure. flue flow, arflow, and hydrocarbon and NOx emssons data. 14

15 1.4 - Plasmatron Operaton Plasmatron Schematc Fgure Schematc of a Plasmaton Fuel Reformer The plasmatron s currently n development at the MT Plasma Fuson Lab. A fuel rch mxture of ndolene and ar s passed through the plasmatron fuel reformer where a hgh voltage spark s used to ntate a partal oxdaton reacton [5]. The deal reacton s: m n n C,,H, +-(O, N,) mco+-h, N, ( ) Ths defnes the best case or deal plasmatron output. n realty some of the CO s overoxdzed to carbon doxde (CO 2 ), resultng n addtonal chemcal energy losses. n addton, a small fracton of the fuel s ether unoxdzed or s oxdzed nto short-chaned hydrocarbons such as methane. Snce the plasmatron s stll n development all of the experments were carred out usng bottled gas that contaned a representatve plasmatron 15

16 output. One gas, whch wll be referred to as the deal plasmatron gas, s based on the above reacton. A second gas, referred to as the typcal plasmatron gas, contans some CO 2 to represent the overoxdaton of CO nto CO 2. Ths typcal plasmatron gas s representatve of the current output that s achevable wth a plasmatron. deal Plasmatron Typcal Plasmatron Hydrogen 25% 23% Carbon Monoxde 26% 21% Ntrogen 49% 52% Carbon Doxde 0% 4% Effcency 85.74% 77.01% Fgure 1.4: deal and Typcal Plasmatron Composton and Effcency Snce the plasmatron s exothermc, the chemcal energy of the plasmatron gas wll be less than the chemcal energy of the ndolene used to generate the plasmatron gas. The plasmatron effcency quantfes these losses and s defned as the Lower Heatng Value (LHV) of the plasmatron gas dvded by the LHV of the ndolene used to generate the gas: 7 7Pl =mh 2 LHVH 2 + mco LHVCO (2) mndolen' LHVndolene r7p,,, = Plasmatron Effcency mx = Mass Flow Rate of component x LHV = Lower Heatng Value 16

17 Chapter 2: Engne Setup and Data Aquston Engne Setup A modfed Rcardo test engne was used to perform the experments. The orgnal cylnder head was replaced wth a modern cylnder head from a Volvo producton engne whle the base engne was unchanged. The followng sheet summarzes the basc engne data: Type Sngle-Cylnder Dual Overhead Cam Bore 83 mm Stroke 90 mm Dsplacement 0.49 L Valves per Cylnder 4 Compresson Rato 10.1:1 Fgure Basc Engne Data n addton, the burn rate of the engne was ncreased by addng a plate nto the ntake system whch partally obstructed the ntake, thereby ncreasng the velocty and turbulence of the ar enterng the engne. Detals of ths modfcaton are presented n Secton ncreasng Burn Rate Engne Control A Motec M4 Engne Control Unt (ECU) model 9806 was used to control the fuel njector pulse wdth (PW) and the spark tmng. The ECU was connected to a dedcated computer that was runnng Motec Engne Management Program Verson Ths setup allowed the PW and spark tmng to be vared n real tme. PW could be vared n ncrements of 0.1 msec and the spark tmng could be vared n ncrements of 1 crank angle degree. 17

18 2.3 - Fuel Data ndolene was used as the reference fuel. The specfc blend used n these experments was Phllps Chevron UTG-96 [6]. A bref summary of the mportant fuel propertes s lsted below: Phllps Chevron UTG-96 Lower Heatng Value (MJ/kg) 43.1 H/C rato (molar) 1.93 Carbon Wt % Hydrogen Wt% Research Octane Number 96.7 Motor Octane Number 87.9 Antknock ndex 92.3 Fgure Selected Fuel Propertes Data Acquston Test Setup n-cylnder To HC Anallyer To NO Analyzer LAF Element Fgure Schematc of the Expermental Setup The schematc n fgure 2.3 shows the overall test cell layout. Ths secton wll dscuss each of the ndvdual methods used to measure arflow, plasmatron flow. ndolene tlow. n-cylnder pressure, and hydrocarbon and NOx emssons. 18

19 Arflow Measurement A Rcardo nstruments Vscous Flow Meter Model #P S was used to measure the arflow. Ths flow meter s a lamnar flow type. n the lamnar flow regme the volumetrc flowrate s smply proportonal to the pressure drop across the element. wth the constant of proportonalty provded by Rcardo nstruments. A custom bult dgtal pressure transducer was used to measure the pressure drop across the element and to convert the pressure drop nto a flowrate ndolene Flow Rate Control A producton Volvo fuel njector, Model # , was used n the engne. The njector was of the sngle-hole type emttng a concal spray. f the pressure drop across a fuel njector s held constant then the flow rate s determned by the njector pulse wdth. To establsh ths relatonshp the njector was removed from the engne and mounted above a chlled graduated cylnder. The Motec ECU software has a calbraton mode where the user can enter the number of cycles to fre and the PW. The njector was fred several thousand tmes at each pulse wdth and the fuel was collected n the graduated cylnder and weghed. Ths was repeated for a range of pulse wdths from 2.0 msec to 20 msec and the relatonshp between pulse wdth and fuel flow per pulse was found to be lnear over the range of nterest. Snce the manfold ar pressure changes wth operatng condtons a fuel backpressure regulator was used to mantan a constant pressure drop across the njector Plasmatron Flow Rate Control To control the plasmatron flow a calbrated crtcal flow orfce was used. For hgh upstream pressures the flow through the orfce s choked and the flow s smply proportonal to the upstream pressure [7]. Choked flow occurs when the upstream pressure exceeds the crtcal pressure, whch can be found from: 19

20 P 2 PCR 7+ (3) P 2 =Pressure Downstream of the Orfce PCR = Crtcal Pressure, Upstream of the Orfce y = Rato of Specfc Heats Evaluatng (3) gves the mnmum upstream pressure that s necessary to guarantee choked flow. All experments were run wth the upstream pressure well above ths mnmum. n the choked flow regme, the flow through the orfce becomes ndependent of the downstream pressure and can be calculated from: y+1 m CDARP 2 (4) CD = Dscharge Coeffcent AT = Area of Orfce Openng t = Pressure Upstream of Orfce R = Gas Constant T = Temperature By settng the upstream pressure of the plasmatron gas the mass flow rate could f controlled. Type B and Type E precson orfces from Flud Control Products were used to control the flow rate of the plasmatron and hydrogen gases. 20

21 Lambda Measurement A heated, wde-band, unversal exhaust gas oxygen senser (UEGO) was used to drectly measure the relatve fuel ar rato n the exhaust stream. The sensor was a Horba MEXA- 1 lo sensor n-cylnder Pressure Measurement A pezo-electrc crystal was used for n-cylnder pressure measurement. A Natonal nstruments BNC-2090 board was connected to a Labvew PC-6025E data acquston board that was nstalled n a PC runnng a Labvew data acquston nterface. A shaft encoder was used to provde the trgger for the pressure measurement. n-cylnder pressure was sampled once per crank angle Hydrocarbon Emssons Measurement The hydrocarbon measurement was taken usng a Rosemont Analytcal Model 402 Hydrocarbon Analyzer. The Rosemont s a Flame onzaton Detector (FD) type analyzer [8]. A FD has a small burner that s fueled by hydrogen gas. The exhaust sample s sent to ths burner and durng the combuston process the hydrocarbon s onzed. An electrode above the flame captures the ons and causes a current to flow through the electrode. Ths current s amplfed and converted to a voltage sgnal. The ampltude of the sgnal s proportonal to the concentraton of the hydrocarbon components. The FD s calbrated usng a certfed reference gas contanng propane. The FD only counts emssons based on C 1 and cannot gve the breakdown of the hydrocarbon composton NOx Emssons Measurement The NOx analyzer was a Thermo Envronment nstruments Model 10 Chemlumnescence NO-NO 2 -NOx detector. The exhaust sample s frst run through a desscant to remove any water vapor n the sample. The sample then enters a reacton chamber where any NOx s converted to NO [9]. The NO s then sent to a chamber where t s reacted wth ozone to form NO, whch s n an excted state. A photon s released when ths molecule rev-erts to the ground state. A photodetector measures the 21

22 ntensty of the sgnal, whch s proportonal to the concentraton of NO. The NO analyzer s calbrated usng a certfed reference gas of known NO concentraton Data Analyss Software An MT propretary bun rate analyss code was used to analyze the raw pressure data [10, 11]. Usng the pressure vs. crankangle data and the geometry of the engne. a pressure vs. volume relatonshp s establshed. The numercal ntegraton of the P-V data then determnes the gross and net ndcated mean effectve pressure (MEP). n addton, f many cycles are used each cycle can be analyzed separately and a coeffcent of varaton (COV) of the NMEP can be calculated. The coeffcent of varaton s smply defned as the standard devaton dvded by the mean. Fnally, by ncorporatng a heat transfer model the pressure data can be used to back calculate the burned fracton as a functon of crank angle.

23 Chapter 3 - Expermental Structure Ths secton wll dscuss how the experments were structured. Ths chapter s organzed nto two man sectons. The frst addresses the experments that were performed to ncrease the burn rate of the engne. The second secton looks at the desgn of the plasmatron and hydrogen addton experments ncreasng Bum Rate As an engne s operated under ncreasngly dlute condtons the burn duraton ncrease due to the effect of the dluents on flame speed [12]. Ths has a negatve mpact on effcency. Snce the experments were explorng lean combuston lmts t was mportant to have an engne wth a fast burnng combuston system. One of the most effectve ways of ncreasng the burn rate of an engne s to ncrease the turbulence level n the engne. A restrctor plate was used on the ntake port of the engne to create addtonal turbulence. Ths method of ncreasng turbulence was chosen because t offered the most flexblty. All of the other methods of ncreasng turbulence, such as alterng the valve profle or port shape, would result n permanent changes to the engne. By usng swappable plates many dfferent turbulence concepts could be quckly tested. n addton, by removng the plate the engne could easly be returned to the base state. 23

24 C1,U.,) 4.) No Plate Plate #1-1/3 Blocked Symmetrc. O "--11 %'- %.-. r 1 C C." Plate #2-2/3 Blocked Symmetrc Plate #3-2/3 Blocked Asymmetrc Fgure ntake Plate Desgns All of the plates ncrease the velocty of the ar by decreasng the cross sectonal area that the ar flows through. The shaded area shows the cross sectonal area through whch ar can flow. The whte area s blocked off. The frst two desgns are ntended to ncrease the amount of tumble ntroduced nto the cylnder. Plate #1 reduces the cross sectonal flow area by 1/3, thereby ncreasng the average velocty of the ar by 50%. Plate #2 s a more aggressve verson of the frst desgn and reduces the cross sectonal area by 2/3. Ths results n the average velocty ncreasng by a factor of three. Plate #3 not only reduces the cross sectonal area by 2/3, but t also bases the arflow to one on the two ntake valves, ntroducng both tumble and swrl nto the cylnder. To test the dfferent plate' concepts a seres of experment were performed. All of the experments were performed usng ndolene as the fuel wthout any plasmatron or hydrogen addton. Frst, the engne was operated wthout the plate and a sweep of ncreasng lambda was performed. At each lambda a spark sweep was performed to fnd the Maxmum Brake Torque (MBT) engne tmng. The data was collected at MBT 24

25 tmng and then lambda was ncreased and the process was repeated. Ths was done untl the engne began to msfre. Fgure 3.2 shows the MBT spark tmng vs. lambda for the unmodfed engne as well as wth each of the three plates n place. The MBT spark tmng s a measure of the relatve burn rates, where faster burnng engnes should have an MBT tmng that s closer to top dead center (TDC). t s clear that all of the plates decrease the burn duraton and ncrease the lean combuston lmt of the engne. The unmodfed engne s the lowest burnng. Plate #1, whch blocks 1/3 of the ntake cross sectonal area. shows a slght mprovement n burn rate although the mpact s modest. On average the MBT tmln moves about 2 degrees closer to TDC. Both of the plates that block 2/3 of the ntake result n the MBT tmng movng sgnfcantly. Ether of these plates would be a good choce for ncreasng the burn rate of the engne. Plate #3 was chosen because t resulted n the fastest burnng rate. The man mpact on burn rate seems to be from the decrease n cross sectonal area and the shape of the plate seems to only have a modest secondary effect. All further experments were performed wth Plate #3 nstalled Plasmatron and Hydrogen Addton Experments Expermental Procedure All of the experments n ths secton were performed n the same manner. ntally the engne was operated stochometrcally and a spark sweep was performed to fnd MBT tmng. Once MBT tmng was found the followng data was taken: n-cylnder pressure. fuel flow, arflow, and hydrocarbon and NOx emssons concentraton. Lambda was ncreased and a spark sweep was agan performed to fnd MBT tmng and the relevalnt data was collected at MBT tmng. Ths processed was repeated, slowly.ncreasnl lambda, untl the engne began to msfre. All experments were performed at 1500RPM and at a NMEP of 350kPa. For each experment the engne was run on one of 4 possble fuel combnatons. establsh a baselne case the frst sweep of lambda was performed usng ndolene onlv. To 25

26 Next the engne was run on a combnaton of ndolene wth one of the plasmatron gases presented n fgure 1.4. Although bottled gases were uses n leu of an actual plasmatron. flow rates and compostons were matched to the case of usng an actual plasmatron. Therefore, the followng schematc s useful n defnng an equvalent percent plasmatron: Plasmatron Engne Concept Fgure Plasmatron Engne Schematc: Arflow and Fuel Flow Plas = Q,dnl = mld LHV,, 1 n,,ll 5( Q,ld + Q,,d2 mrnd LHV,,d m + lnd2 LH,,J md,l, +,,d 2 From (5) t s clear that the equvalent percent plasmatron s smply the mass fracton of the ndolene that s sent through the plasmatron. Three sweeps of lambda were performed for the typcal plasmatron gas, matchng the flows approprately to represent 10%. 2r0%. and 30% reformed plasmatron gas. The next experment was done usng the deal plasmatron gas at 10%, 20%, and 30% reformed fractons. Ths would provde a way to quantfy the potental gans that could come from optmzng the plasmatron. Fnally. experments were performed substtutng hydrogen for plasmatron gas to separate out the f 26

27 mpact of the carbon monoxde, carbon doxde, and ntrogen present n the plasmatron gas Equvalent Percent Plasmatron Defnton Before any hydrogen addton experments could be performed an approprate defnton of the equvalent percent hydrogen had to be formed so that the hydrogen experments would be comparable to the plasmatron experments. Fgure 3.4 helps explan the ratonal used n defnng the equvalent percent plasmatron for the drect hydrogen addton experments. Expermental Setup - Equvalent a) Hydroqen Only Addton b) Fgure Expermental Setup for Plasmatron and Hydrogen Addton Fgure 1.2 ntroduced t schematc of the expermental setup. Snce the ndolene. ar. and plasmatron gas are homogeneously mxed pror to enterng the engne the schematc n 3.4a s an equvalent representaton. The only reason the schematc s shown n ths new confguraton s to hghlght the smlartes between the plasmatron and hydrogen addton experments. Fgure 1.1 presented data on the burn characterstcs of CO. At 27

28 stochometrc condtons the lamnar flame speed of CO s somewhat slower than a typcal hydrocarbon. However, the maxmum flame speed and the dluton lmt are both somewhat hgher. Therefore t s unclear whether the CO wll have postve or a negatve mpact on combuston when compared to a hydrocarbon. Snce the burn characterstcs of CO are smlar to a hydrocarbon t wll be grouped wth the ndolene n the schematc and for the purpose of analyss. Thd analyss of the data wll show that ths s a reasonable assumpton. The equvalent percent hydrogen should be defned n such a way that a drect comparson between the plasmatron and hydrogen only cases quantfes the effect of the plasmatron components other than the hydrogen. From Fgure 3.4 t s clear that matchng the fracton of the total energy that s provded by the hydrogen wll allow for a vald comparson. Fgure 3.5 s an energy balance on the plasmatron and wll ad n dervng the equatons for the equvalent percent plasmatron. Although bottled gases were used all flow rate were matched so that a comparson to the fgure 3.5 s vald. Plasmatron - Energy Balance Ar Fgure Energy Balance on System Usng a Plasmatron From fgure 3.5 we can form a rato of the energy provded by the engne to the total energy enterng the engne: QH2 QH2 eq x -7pls H X.rPL 4s H (6) Qengnze QPLAs + QNVDOLENVE QX./7PLAS +Q (1-X ) 1+ X(PLAS -1) 28

29 Where: Q = heatng value /7PuS = (see Fgure 1.4) H = fracton of the energy n the plasmatrop gas that s suppled by hydrogen X = Equvalent Percent Plasmatron H n2'mwh 2 2 LHVH2 (7) nc ' MWco LHVco All of the varables on the rght hand sde of (7) are known and the equaton then gves H= Fnally, nsertng the numercal values for 77pAs and H nto (6) gves: QH? X (8 Qengne X Equaton (8) can be used to calculate the fracton of the total energy enterng the engne that should be provded by hydrogen to match a certan deal plasmatron run. For example, X=10% gves 3.93% as the fracton of the total energy provded by hydrogen. n other words, settng the hydrogen energy fracton equal to 3.93% n a hydrogen addton experments wll provde an equvalent percent plasmatron of 10%. Notce ths dervaton makes no menton of lambda, but only dscusses equvalent percent plasmatron. From the daram t can be seen that the extra N 2 /CO, act as an extra dluent. At the same lambda the plasmatron cases wll be more dlute than the hydrogen addton only cases. Therefore, lambda no longer reflects the true dluton of the tuel/ar mxture n the cylnder. The next secton wll dscuss ths ssue and wll ntroduce a new dluton parameter that s more approprate. 29

30 Dluton Parameters When examnng lean combuston lambda s often used as the ndependent varable aganst whch data s correlated or plotted. Lambda approprately represents the normalzed ar/fuel rato though t does not nclude the addtonal dluton of the resdual burned gas. f the engne s beng run on a sngle fuel and no EGR s beng used then lambda defnes the relatve dluton. f EGR or multple fuels are used then lambda wll not gve the true dluton. n these cases where lambda does not defne the dluton. a dluton parameter that represents true dluton of the mxture would be useful. From Fgure 3.4 t s seen that at the same lambda the plasmatron cases wll be more dlute then the hydrogen addton case due to the excess N 2 and CO 2. Burn duraton s a basc combuston parameter that can be useful n quantfyng the effect of dluton snce t s prmarly affected by engne operatng condtons, fuel type, and dluton. All of the experments were operated under the same engne operatng condtons and the hydrogen levels were matched n such a way as to provde an equvalent percent plasmatron. Therefore, f an approprate dluton parameter s formed a drect comparson of the burn duraton under the deal plasmatron, typcal plasmatron, and hydrogen experments wll be possble. Ths new dluton parameter should replace lambda and extend to all analyss, not just burn duraton. t s recognzed that ths dscusson s a smplfcaton of the factors that mpact burn duraton. For example, although all of the experments were done under the same speed and load condtons the total mass flow rate vared slghtly dependng on whether plasmatron or hydrogen gas was used. Therefore, the turbulence n the engne wll vary slghtly, mpactng bu duraton. Tryng to account for these secondary effects would greatly ncrease the complexty of the analyss. n addton, these secondary affects are often dffcult to quantfy. t wll be shown that gnorng these secondary effects does not have a detrmental mpact on the analyss. Fgure 3.6 shows the 0-l.0% burn angles for the deal plasmatron and hydrogen cases vs. lambda. As expected the burn duratons at a fxed lambda are longer for the plasmatron cases then for the equvalent hydrogen addton case. The extra dluton suppled by the 30

31 N 2 and CO 2 n the plasmatron gas slows combuston. An approprate dluton parameter would account for ths extra dluton. One smple dluton parameter s the heatng value of the fuel per unt volume of fuel/ar mxture. Ths wll be referred to as the volumetrc dluton parameter (VDP-*): Q= ms LHVj.. (9) mnd M plas Mar MWno + =MW -MW MWnd MW plus MW ar (10) n,o, = Total molar flow rate nto the engne MW = Average Molecular Weght From the deal gas law: nrt V-P P (11) Then the energy per unt volume, VDP*, s smply: VDP* = Q V (12) For convenence, a dmensonless Volumetrc Dluton Parameter (VDP) was defned relatve to the stochometrc, gasolne only case: 31

32 VDP = VDPndolene-onl.anmbda= (13) VDP* Fgure 3.7 shows the same 0%-10% burn angle data plotted aganst the VDP nstead of lambda. The VDP calculaton does a good job of collapsng the burn duraton data. At the 10% equvalent plasmatron level the ft between the deal plasmatron and hydrogen addton s excellent. At the 20% level and 30% levels the deal plasmatron experments burn faster than the drect hydrogen addton experments at the same VDP. One reason for ths dscrepancy s that the VDP does not take nto account the affect of heat capacty. Components that have a hgh heat capacty wll absorb more thermal energy then components that have a low heat capacty and therefore wll have a larger dluton effect. ncorporatng the heat capacty n the dluton parameter should mprove the dluton parameter. f an energy balance s done on the system: Qconmb = m LHV (14) Qcomb = Chemcal Energy Released Durng Combuston f the combuston process s modeled as constant volume and the change n composton durng the combuston process s gnored, then the heat released wll be equal to the heat absorbed by the gas: Qcomb =m m,, v AT (15) Settng (14) equal to (15) and solvng for AT gves: 32

33 m LHVj AT= (16) mtot Cv AT s the chemcal energy per unt heat capacty and thus represents the thermal dluton of the mxture. Snce the change n specfc heat of the gases was gnored AT s not exactly the adabatc, constant volume temperature dfference between the burned and unburned gases due to combuston. However, t approxmates that number. Many of the combuston related processes should scale well wth ths varable. For example. the flame speed s largely determned by the temperature rse across the flame. Therefore. there should be a strong correlaton between burn rate and AT. t s useful to convert the AT to a dmensonless Thermal Dluton Parameter (TDP) whch s defned n the same manner as the VDP. TDP ATndolene onl,lambda=l (17) AT Fgure 3.8 shows the same bum duraton data plotted aganst TDP. At the 10% and 20% levels the deal plasmatron and hydrogen addton experments gve very smlar results. At the 30% level the plasmatron s faster burnng at an equvalent TDP. Ths mples that the CO and N 2 n the plasmatron gas have a postve mpact on the combuston process. Ths s thought to be due to the hgher dluton lmt of CO when compared to a hydrocarbon. Both the VDP and TDP are straghtforward to calculate and provde a better correlaton wth the data. t s mportant that the correct dluton parameter s chosen when analyzng the data. Most parameters such as burn duraton, combuston stablty. combuston effcency, and NO emssons depend on thermal dluton and therefore wll be dsplayed 33

34 aganst TDP. However, one mportant phenomena, the pumpng work, s based on the volumetrc flowrate of the gas through the engne and therefore should correlate more closely wth VDP. Net effcency s dependent on pumpng work and wll therefore be plotted aganst VDP. t s clear that the choce of whether to use TDP or VDP s dependent upon the specfc parameter beng analyzed. All TDP and VDP graphs that are not presented n the body of the paper are avalable n the appendx. To summarze, n order to provde a useful comparson between the typcal plasmatron. deal plasmaton, and hydrogen addton experments t was necessary to formulate some new parameters. Frst, an equvalent percent plasmaton was defned for the hydrogen addton cases. n addton, two dluton parameters based on volumetrc and thermal dluton were defned. Usng the equvalent percent plasmatron along wth the VDP or TDP dluton parameter wll allow a useful comparson of the data for the dfferent fuelng schemes. 34

35 MBT Spark Tmng vs. Lambda E 40 co :m (n LC"CCCCCCCCCCCCCCCCC ""- "A/ / --- Plate #1 - -Plate #2 -- e-plate #3 -: No Plate : Lambda 1.9, Fgure #3.2 - MBT Spark Tmng vs. Lambda for Dfferent ntake Plates Desgns 0%-10% Burn Angle vs. Lambda ou a5 45 < S Add = 10% Equv -12 Add = 20% Equv -2 Add = 30% Equv deal Plas = 10% deal Plas = 20% deal Plas = 30% ndolene Only Lambda Fgure #3.6-0%-10% Burn Angles vs. Lambda - deal Plasmatron and Hydrogen Addton 35

36 - 0%-10% Burn Angle vs. VDP 50 fld / J,1+ 1 7,, *~~~~ ' l t 1. L_ m o ọ 0 CD >u"-r 0S~~~~~~~eR '..s ~.0 7 /,,' 1)"j--- --, r~~~~~~~~~~ r ' O~~~~~~ --- H2 Add = 10% Equv -- H2 Add = 20% Equv - H2 Add = 30% Equv -- -~::- -deal Plas = 10% deal Plas = 20% deal Plas = 30% ndolene Only 15 c, Dluton Scale - VDP Fgure #3.7-0%-10% Burn Angles vs. VDP - deal Plasmatron and Hydrogen Addton 50 0%-10% Burn Angle vs. TDP 4) C 35 4 C 30 m n v ;?, 4/ l' Dluton Scale - TDP t0 ~ - -- H2 Add = 10% Equv H2 Add = 20% Equv -- H2 Add = 30% Equv - - * - - deal Plas = 10% deal Plas = 20% deal Plas = 30% x---- ndolene Only 2 Fgure #3.8-0%-10% Burn Angles vs. TDP for deal Plasmatron and Hydrogen Addton 36

37 Chapter 4 - Results and Dscusson As stated earler a total of 10 sets of experments were performed: deal plasmatron. typcal plasmatron, and hydrogen addton at 10%, 20%, and 30% equvalent percent plasmatron levels as well as one experment usng gasolne only. Frst, an error analyss wll be used to establsh the level of accuracy of the fuel and arflow rate. Next the results wll be presented for all 10 sets of experments: MBT spark tmng, burn duraton data, combuston varablty, hydrocarbon emssons, engne only effcency, overall fuel system effcency whch takes nto account the plasmatron losses, and fnally NOx emssons. Where t s approprate the data wll be presented on both a tradtonal lambda scale as well as an approprate dluton scale Error Analyss Snce one of the prmary goals of the experment was to determne the fuel converson effcency under dfferent fuelng strateges t was mportant to perform an error analyss to determne the level of accuracy n the arflow and fuelflow. The mass flow rates of the ndolene, plasmatron (or hydrogen), and ar were all measured ndependently. n addton the lambda of the exhaust stream was measured drectly. Therefore lambda ould be calculated from the flow rates and compared to the lambda measured drectly wth the UEGO. Fgure 4.1 shows ths graphs of UEGO Lambda vs. Calculated Lambda. The UEGO lambda and calculated lambda match up well for all experments and across the entre operatng range. An absolute percent error can be defned as: Absolute _ % _ Error = EGO - ace (18) kuego 37

38 Fgure 4.2 s a graph of absolute percent error versus lambda. The error seems to be random and does not exhbt any obvous trends. The average error s 1.51 % and the maxmum error s 3.21% MBT Tmng MBT tmng s a famlar varable and s a good ndcator of relatve burn duratons. Fgure 4.3 shows the MBT spark tmng for the typcal and deal plasmatron experments. At a fxed lambda the MBT tmng moves closer to top dead center as more plasmatron gas s added. The match between the deal and typcal plasmatron data s excellent at all equvalent percent plasmatron levels. Fgure 4.4 shows the same MBT spark tmng data plotted aganst TDP. As expected the correlaton between the data s better when plotted aganst TDP. Fgures 4.5 and 4.6 compare the MBT spark tmng of the deal plasmatron and hydrogen addton cases. Fgure 4.5 shows that at the same lambda the hydrogen addton experments burn sgnfcantly faster than the plasmatron addton experments. Ths s due to the extra dluton caused by the N 2 n the deal plasmatron gas, whch s not present n the hydrogen addton experments. When shown on the TDP scale, whch more accurately represents dluton, the 10% and 20% curves algn almost perfectly. n addton, at the 30% equvalent plasmatron level the deal plasmatron s slghtly faster burnng than the drect H 2 addton. Ths shows that usng a plasmatron to produce the H 2 onboard does not have a detremental effect on combuston, but nstead results n combuston that s at least as fast and s some cases faster than the drect hydrogen addton Burn Duraton n secton t was argued that burn duraton should be should be strongly dependent on thermal dluton. Fgure 4.7 shows the 0%-10% burn duraton for the typcal and deal plasmatron plotted aganst lambda. At low values of lambda the combuston process s both fast and stable and the addton of plasmatron gas has only a small mpact on burn duraton. For example, at a lambda of 1.0 the spread n the 0%-10% burn duraton s only 38

39 3 degrees. As the dluton level ncreases the curves begn to separate as the hydrogen n the plasmatron has an ncreasngly postve effect on the combuston process. At a lambda of 1.6 the spread s 13 degrees. The mpact of burn duraton on effcency s expected to grow as lambda s ncreased. Lookng at the typcal and deal plasmatron trals the match n burn duraton s good although as lambda s ncreased the deal plasmatron burns faster than the typcal plasmatron. Ths can agan be explaned through dluton snce the typcal plasmatron s more dlute than the deal plasmatron at an equvalent lambda. Fgure 4.8 shows the same data plotted aganst TDP, whch properly accounts for dluton. The typcal and deal plasmatron data now match up better than they had when plotted aganst lambda. Althought the 10%-90% burn rate data s a less stable parameter and therefore more dffcult to draw conclusons from, t s clear from fgure 4.9 that at a fxed lambda the burn duratons for the deal plasmatron gas are generally shorter than for the typcal plasmatron gas. n fgure 4.10, when plotted aganst TDP, the deal plasmatron no longer exhbts a shorter burn duraton at the same equvalent percent plasmatron. The burn rate data suggests that effcency should ncrease wth ncreasng plasmatron amounts, although the effect wll be small at low dluton levels and ncreasngly mportant as dluton levels ncrease. The 0%-10% deal plasmatron vs. hydrogen data was already dscussed when dervng the dluton parameters. t was shown that the plasmatron addton was slghtly faster burnng than the hydrogen addton when compared at a fxed TDP. The 10%-90% burn duraton s shown n fgures 4.11 and A smlar concluson can be drawn from ths data. The hydrogen addton s sgnfcantly better at decreasng burn duraton at fxed lambda. When dluton s properly accounted for the plasmatron addton seems to result n slghtly faster combuston although varablty n the data makes t dffcult to nterpret. n concluson the TDP parameter has proven to be useful n analyzng the burn duraton data. When the burn rate data s plotted vs. lambda each burn profle forms a separate curve and a drect comparson between the hydrogen addton and the plasmatron 39