DF-PCCI: Concept Development of New Diesel Dual Fuel Technology for Diesel Common-Rail Light Duty Pickup Truck

DF-PCCI: Concept Development of New Diesel Dual Fuel Technology for Diesel Common-Rail Light Duty Pickup Truck Krisada Wannatong, Somchai Siengsanorh and Nirod Akarapanyavit PTT Research and Technology Institute, PTT Public Company ABSTRACT Diesel dual fuel (DDF) is an alternative combustion technology which can be implemented for a conversion of diesel engine to fuel by natural gas. In DDF technology, natural gas cannot be used as a soul fuel; some of diesel fuel is still needed. However, only a little portion of diesel can be replaced by natural gas (so called energy replacement) and the engine efficiency is very low with extremely high methane emission. In order to support the use of natural gas, PTT Public Company Limited has been developing new DDF technology named DF-PCCI. With this technology, the exhaust gas recirculation (EGR), throttle and diesel injection strategies were optimized. This paper presents the development methodology of the DF-PCCI pickup truck (concept development phase). INTRODUCTION Natural gas is a promising alternative fuel for many reasons. It has been successfully utilized in ground transportation sector. The engine type which is mainly used for ground transportation can be classified in to two portions: spark ignition and compression ignition engine. The former one has been successfully utilized due to the similarity of fuel properties and gasoline fuel. Examples are the utilizing of natural gas in passenger car by bifuel technology and the utilizing of natural gas in heavy duty truck by dedicated technology. However, for the compression ignition engine which has high compression ratio, natural gas cannot used as the sole fuel because of the engine knock limitation. So, the dual fuel technique has been utilized instead. In dual fuel engines, the main fuel is introduced either homogenously by mixer or port injectors in the air intake, or is directly injected in the combustion chamber. The injected pilot fuel serves as an ignition source. The dual fuel engine is so called diesel dual fuel (DDF) if the diesel is used as the pilot fuel [1,2]. Some challenges for DDF development especially for light-duty pickup truck are the poor thermal efficiency and high emission at part load and engine knock at high load [3,4]. These poor characteristics limit the energy replacement. Only 50% energy replacement can be made by the best available DDF technology for passenger car (evaluated under New European Driving Cycle, NEDC) [5]. Moreover, its exhaust emissions and the conversion cost from normal diesel engine to DDF engine are still not reasonable. It is not surprising that there are no technologies available for application of natural gas in light duty diesel situation. From the above reasons PTT public company limited has to take accountability and responsibility to develop the DDF technology for diesel common rail pickup truck regarding to improve the engine efficiency, exhausted emission and energy replacement. The target is the new DDF technology with at least 60% energy replacement NEDC, higher engine efficiency, and cleaner exhaust emission. The state of problem described above can be summarized to a mind map as shown in Fig. 1. Bi-fuel Conversion (After market) Bi-fuel OEM Dedicated Gas Engine OEM Diesel converted To Gas Engine (After market) Gasoline Passenger Car Natural Gas Application In Transportation Heavy Duty Truck Solutions are available for application in spark ignition concept Diesel Pickup Truck New DDF Tech. is Needed Simple DDF (After market) Simple DDF? OEM Solution is not available for application in compression ignition concept DF-PCCI Developed by PTT-RTI DF-PCCI has been developed to be the best solution for application of natural gas in compression ignition concept Fig.1 DDF motivation mind map. Low efficiency Low replacement High THC emission Acceptable efficiency Low replacement High THC emission Target Eff.~Diesel Rep. =60% Emission ~EURO3 Cost ~ 70,000 Baht Technology to OEM Technology to After market

The success of this project will be the significant driver to promote the use of natural gas for Thailand s future transportation. This paper presents the PTT s development methodology of DDF engine which is divided into three sections: 1) the summary of feasibility studies, 2) the DDF concept development and 3) the concept DDF vehicle evaluation. SUMMARY OF FEASIBILITY STUDIES VEHICLE AND ENGINE SELECTION A light duty pickup truck powered by 2.5 liter diesel common-rail engine was selected for this DDF engine development. The reason is the highest market share in Thailand diesel light duty market. The specification of selected engine is shown in Appendix Table A1. ACTUATORS SELECTION For a selected diesel common-rail engine, controllable actuators which have effect on combustion are injectors, EGR valve, throttle valve and common-rail pressure. A literature of effects of these actuators on engine performance and exhaust emission are as follows. Effects of Injection Parameters There are 3 patterns of injection considered: late start of injection (SOI), early SOI, and dual pilot injection. Considering late SOI at low load [6], retarded injection timing resulted in lower thermal efficiency and hydrocarbon (HC), but yielded lower NOx emission [7]. At advanced injection timing, the opposite in results was observed. Heavy knock was also observed during the advanced injection timing [8]. Considering early SOI at low load, NOx emission substantially decreases when applied the highly advanced timing. However, the cycle by cycle variations were increased [9]. Dual pilot injection is a combination of early SOI and late SOI. It was successfully reduce HC emission at low load [10]. fuel air mixture is lean. To prevent the quenching of flame propagation, the intake air is reduced by throttling. Even though the pumping losses are increased in throttling process, it is overcome by an increase in the combustion efficiency [9]. Effects of EGR The use of EGR has been widely recognized as an effective way to control NOx emission in internal combustion engines. The rate of NOx formation grows rapidly at high temperatures (> 1800 K). In engines, combustion temperatures below 2000 K are suggested to avoid high NOx engine-out emissions [11]. EGR diluents reduce the combustion temperatures as a combined result of a lower O 2 concentration and a lower specific heat ratio of the mixture. Hot EGR is considered to be the best alternative for improving low load characteristics [12]. The hot EGR heats up the intake mixture and the unburned hydrocarbon from previous cycle can be re-burnt. So, both thermal efficiency and NO X emissions can be improved at the same time. STUDY OF DIESEL OPERATING CONDITION UNDER NEW EUROPEAN DRIVING CYCLE (NEDC) The NEDC (as shown in Fig.2) is the driving cycle which is used for vehicle emission evaluation. There are plenty of engine operating conditions such as idle, low load and high load are included. Wannatong, et al [13] performed a vehicle test on chassis dynamometer to search the engine operating condition which often used in NEDC. In this test, the engine was equipped with a combustion indicating system in order to measure an indicated mean effective pressure (IMEP) of the engine during driving with NEDC. Results from this study are shown in Fig.3. From the vehicle test results, it was found that, under NEDC, this engine was often operated at low load and medium speed. So, most research works in the DDF development project focus on this operating condition. Effects of Throttling The problem related to low loads in DDF is the limitation of flame propagation as the gaseous

Fig.2 vehicle speed and engine speed during operates the 2.5 liter diesel engine under NEDC. Fig.4 In-cylinder pressure histories for different injection timings. : DDF 1600 rpm, NG = 0.31 kg/h, diesel = 0.10 kg/h, single-pulse diesel injection. Fig.3 distribution of indicated mean effective pressure (IMEP) during operates the 2.5 liter diesel engine under NEDC. STUDY OF DIESEL INJECTION STRATIGIES FOR DIESEL DUAL FUEL COMBUSTION FOR LOW LOAD OPERATING CONDITION The literature shows that the injection parameters have significantly effects on DDF combustion characteristics. In order to learn more that how it affects combustion characteristics, Aroonsrisopon, et al [15] performed a test on single cylinder engine (Ricardo Hydra) which modified to DDF diesel common-rail engine. The engine was operated at low load and medium speed condition. Effects of diesel injection parameters on combustion and its emission were investigated. Here is only the effects of diesel injection timing on combustion and its emission at speed 1600 rpm, NG = 0.31 kg/h, diesel = 0.10 kg/h, single-pulse diesel injection is selected to review. The specification of this engine and natural gas properties are shown in Appendix Table A2 and Table A3, respectively. Fig.5 IMEP, COV of IMEP, pressure rise rate, and maximum in-cylinder pressure for different injection timings. :DDF 1600 rpm, NG = 0.31 kg/h, diesel = 0.10 kg/h, single-pulse diesel injection.

Wannatong, et al [14]. In this study, the 2.5 liter diesel common-rail engine was modified to DDF engine. More detail of experimental is given in [14].The was operated at low load and medium speed (2 bar IMEP, 2000 rpm). Four matrix test was performed including the base diesel operation, the simple DDF, the DDF concept 1 and DDF concept 2. For DDF mode, the ratio between gas energy and diesel energy was set to 0.7. In the base diesel mode, all control parameters were operated at the same condition as typical diesel common-rail. In the simple DDF mode, only diesel fuel was reduced. All actuator still be the same as diesel operating condition. In DDF concept 1, the diesel injection timings were set to the best operating condition mean while the EGR and throttling was the same as diesel operating condition. In the DDF concept 2, diesel injection timings, EGR and throttle were set to the best DDF operating condition. Fig.6 NOx, CO, THC, and methane emissions for different injection timings.: DDF 1600 rpm, NG = 0.31 kg/h, diesel =0.10 kg/h, single-pulse diesel injection. Fig. 4, Fig.5 and Fig.6 show the pressure histories, combustion characteristics and emission restively for different injection timings. DDF 1600 rpm, NG = 0.31 kg/h, diesel = 0.10 kg/h, single-pulse diesel injection. It was found that all combustion characteristics and also their emissions were changed during the retard injection timing process. From these results, the promising injection timing (best IMEP and less NOx and HC emissions) is about 45 degree before top dead center (BTDC). It should be noted that this injection timing is totally difference with typical diesel common-rail injection timing. So, in order to operate the DDF engine, the full control of injection parameters is really needed. DEVELOPMENT OF NEW DIESEL DUAL FUEL COMBUSTION CONCEPT FOR LOW LOAD OPERATING CONDITION Knowledge from literatures, diesel operating condition under NEDC and also from diesel injection strategy was implemented in this study, the new diesel dual fuel combustion concept for low load operating condition by The comparison of diesel injection timing between diesel mode, simple DDF mode and new DDF mode (used in concept 1 and concept 2) is shown in Fig.7. Input Air + EGR Air + Gas Air + EGR TDC Intake Gas 70% -270 CA Diesel 1 st pulse, 27%, -50 CA BDC Compress TDC Combust Diesel 100% 1st pulse, -15 CA Diesel 30-50% 1st pulse, -15 CA Diesel 2 nd pulse, 3%, -15 CA BDC Exhaust Diesel Simple DDF DF-PCCI Fig.7 Comparison of diesel injection timing between diesel mode, simple DDF mode and new DDF mode (used in concept 1 and concept 2). TDC Fig.8, Fig.9 and Fig.10 show the engine brake efficiency, methane emission and NOx emission comparison between base diesel, simple DDF, DDF concept 1 and DDF concept 2. It was found that the DDF concept 2 is the best. So, the DDF concept 2 is in the progress of patenting as DF-PCCI.

NOX (ppm) Methane (ppmc1) Brake Efficiency (%) The 7 th International Conference on Automotive Engineering (ICAE-7) 30 25 control algorithms, and 4) the concept of DF- PCCI light duty truck. 20 15 10 5 0 Simple conversion Concept 1 Concept 2 Baseline Diesel Fig.8 Comparison of engine brake efficiency between diesel mode, simple DDF mode, DDF concept 1 mode and DDF concept 2 mode. 10000 9000 8000 7000 6000 5000 4000 3000 2000 1000 0 Simple conversion Concept 1 Concept 2 Baseline Diesel ENGINE CONTROL ARCHITECTURE AND ENGINE CONTROL ALGORITHMS The engine control architecture of DF-PCCI concept is shown in Fig.11. From the figure, there are at least three existing diesel actuators that have to be controlled in order to implement the DF-PCCI concept into the diesel common-rail engine, throttle valve, EGR valve and diesel injectors. Moreover, new gas injector needs to be installed into the intake manifold. In the concept development phase, the original OEM ECU was fully replaced by research crio ECU which capable to control all actuators mention above. Fig.9 Comparison of methane emission between diesel mode, simple DDF mode, DDF concept 1 mode and DDF concept 2 mode. 45 40 35 30 25 20 15 10 5 0 Simple conversion Concept 1 Concept 2 Baseline Diesel Fig.10 Comparison of NO X emission between diesel mode, simple DDF mode, DDF concept 1 mode and DDF concept 2 mode. DEVELOPMENT OF DF-PCCI CONCEPT FOR LIGHT DUTY TRUCK In the previous section, the feasibility studies of new DDF combustion concept (DF-PCCI) were proposed. The last status of DDF engine after feasibility is the DDF engine operated with the DF-PCCI concept but only steady state. In order to implement the DF-PCCI in the vehicle, the engine control unit (ECU) development is needed. Four topics are selected to be presented in this paper: 1) the development of engine control architecture, 2) the steady state engine calibration, 3) engine Fig.11 DDF engine control architecture. STEADY STATE ENGINE CALIBRATION There are several engine operating conditions used during driving the vehicle in NEDC. So, the set value of each actuator for each operating condition has to be defined or calibrated. For this development, the calibration process is shown in Fig.12. The process starts with the implementation of DF- PCCI concept into each operating point. Then the design of experiment technique (DOE) was designed in order to reduce the calibration point. The engine was tested by following the DOE plan. The measurement data from each test would be modeled and optimized after that. Finally, the optimized set point for each actuator and for each operating point would be filled into the map.

DDF Concept DOE Engine Test Measurement & Evaluation Model & Optimization Map Generation Fig.12 Steady state engine calibration process for DF-PCCI engine. Since there are several actuators and several operating conditions, several maps are needed. Fig.13 shows how all maps were utilized in the engine control algorithms. The algorithm starts when the ECU gets the demand signal from the pedal. Then the energy that matches the demand will be designed. After that, the combustion zone, the energy replacement and the air fuel ratio were set as the control target. The throttle valve position, EGR valve position and rail pressure will be controlled until the energy replacement, air fuel ratio and others reach the target. In order to control the air fuel ratio, EGR valve, rail pressure and throttle valve, the simple PID control technique was utilized. Pedal OEM ECU COMMUNICATION crio ECU Fig.14 Communication of OEM and crio ECU in DF-PCCI light duty truck (concept development phase). Fig.15 Position of gas equipments in DF-PCCI light duty truck (concept development phase). Engine Speed Zone Energy needed Replacement Gas injection Gas Pressure & duration Gas Injection EVALUATION OF PROTOTYPE DF-PCCI LIGHT DUTY TRUCK UNDER NEDC Lambda Needed EGR TPS Lambda Control EGR PID Control TPS PID Control Rail pressure Rail pressure Sliding Mode Control Control Algorithms Development 1 st pulse Diesel injection timing 2 nd pulse Diesel injection timing Diesel Duration Diesel Duration ECT Compensate AIT Compensate Fig.13 DF-PCCI engine control algorithms (concept development phase). DF-PCCI LIGHT DUTY TRUCK (CONCEPT DEVELOPMET PHASE) Diesel Injection The engine control unit (crio) with control algorithms software was installed into the vehicle. The OEM ECU was fully replaced by crio ECU. However, it is very easy to go back with OEM ECU because the connections of both ECUs are the same. The positions of crio ECU and OEM ECU are shown in Fig.14. The other DF-PCCI equipments in the DF- PCCI light duty pickup truck are shown in Fig.15. The DF-PCCI vehicle was evaluated under NEDC. Six tests were performed as shown in Table 1. It should be noted that 1. vehicle in test No 3 was from OEM. 2. vehicle in test No 1,2,4,5 and 6 was the same diesel common-rail pickup truck with different modifications. 3. the energy replacement during NEDC is difficult to be controlled because of the transient operating condition. Table 1. DDF Vehicle Evaluation test matrix Test No Mode Replacement (%) 1 Diesel 0 2 DDF-Simple 54 3 DDF-Simple-OEM 48 4 DF-PCCI RE46 46 5 DF-PCCI RE62 62 6 DF-PCCI RE64 64 Fig.16 shows the DDF vehicle evaluation results. From the results, THC and CO emissions from Simple DDF are the highest.

Emission (g/km), Replacement ratio (DieselDDF/Diesel) The 7 th International Conference on Automotive Engineering (ICAE-7) These emissions were still high in OEM vehicle. Consider the DF-PCCI test results, more replacement gave more exhaust emissions. However, even the highest replacement (64%), it was still lower than the simple DDF. The results show that the exhaust emissions were improved significantly by DF-PCCI concept. 6 5 4 3 2 1 0 EURO3 Diesel DF-PCCI-RE46 DF-PCCI-RE62 DF-PCCI-RE64 OEM-Simple DDF-RE54 OEM-CR DDF-RE48 Replacement THC CO NOx Fig.16 DDF vehicle evaluation results. CONCLUSTION The methodology of DF-PCCI concept development and it implementation in light duty pickup truck were proposed. The significant improvement in exhaust emission shows the success of the project. FURTHER WORK In the concept development, the research crio ECU was used as the engine control unit. The development of ECU which is commercial ready is the next step of this development. ACKNOWLEDGMENTS The authors would like to acknowledge the financial and technical support of PTT Public Company Limited (Thailand) and Kasetsart University (Thailand). REFERENCES 1. Wannatong,K. Natural Gas Application in Thailand: Locomotive and Fishing Boat, GASEX Conference, Biejing, 2006 2. Hsu, B.D. Practical Diesel-Engine Combustion Analysis, SAE International, 2002 3. Karim, G.A., Combustion in Gas Fuelled Compression-Ignition Engines, ASME ICE Fall Technical Conference, 351, 2000 4. Wannatong, K., Akarapanjavit, N., Siangsanorh, S., and Chanchaona, S., Combustion and Knock Characteristics of Natural Gas Diesel Dual Fuel Engine, SAE Technical Paper No. 2007-01-2047, 2007. 5. Thummadatsak, T., DDF Evaluation, Internal Publications in PTT Company Limited, 2007. 6. Talus, P., Richard, J.A., Nigel, N.C., Michael, L.T., Christopher, M.A., Operation of a compression ignition engine with a HEUI injection system on natural gas with diesel pilot injection, SAE paper 1999-01- 3522 7. Shen, J., Qin, J, Yao, M., Turbocharged diesel/cng Dual-fuel Engines with Intercooler: Combustion, Emissions and Performance, SAE paper 2003-01-3082 8. Singh, S., Krishnan, S.R., Srinivasan, K.K., Midkiff, K.C., Effect of pilot injection timing, pilot quantity and intake charge conditions on performance and emissions for an advanced low-pilot-ignited natural gas engine, Int. J. Engine Research Vol. 5 No. 4, 2004 9. Micklow, G.J., Gong, W., Mechanism of hydrocarbon reduction using multiple injection in a natural gas fuelled/micro-pilot diesel ignition engine, Int. J. Engine Research Vol. 3 No. 1, 2002 10. Daisho, Y., Yaeo, T., Koseki, K., Saito, T., Kihara, R., Quiros, E.N., Combustion and Exhaust Emissions in a Direct-Injection Diesel Engine Dual-Fuelled with Natural Gas, SAE paper 950465 11. Christensen, M., Johansson, B., and Einewall, P., Homogeneous Charge Compression Ignition (HCCI) Using Isooctane, Ethanol, and Natural Gas A Comparison with Spark Ignition Operation, SAE Paper 972874 12. Daisho, Y., Takahashi, K., Iwashiro, Y., Nakayama, S., Kihara, R., Saito, Controlling Combustion and Exhaust Emissions in a Direct-Injection Diesel Engine Dual-Fuelled with Natural Gas, SAE paper 952436 13. Wannatong, K., Akarapanjavit, N., Siangsanorh, S., Aroonsrisoporn, T., and Chanchaona, S., New Diesel Dual Fuel Concepts: Part Load Improvement, SAE Technical Paper No. 2009-01-1797, 2009. 14. Aroonsrisopon, T., Salad, M., Wirojsakunchai, C., Wannatong, K., Akarapanjavit, N., Siangsanorh, S., Injection Strategies for Operational Improvement of Diesel Dual Fuel Engines

under Low Load Conditions, SAE Technical Paper No. 2009-01-1855, 2009. CONTACT Dr. Krisada Wannatong PTT Public Company Limited. Email: krisada.w@pttplc.com APPENDIX Table A1. 2.5 Liter diesel common-rail engine specifications. Number of cylinders: 4 (inline) Number of valves: 16 (DOHC) Manifold: Cross-flow with turbocharger Fuel system: Common rail direct injection Displacement: 2,494 cc Bore: 92.0 mm Stroke: 93.8 mm Connecting rod: 158.5 mm Compression ratio: 18.5:1 Max power: 75 kw at 3,600 rpm Max torque: 260 N m at 1,600 2,400 rpm Valve timings: IVO IVC EVO EVC 718 CA 211 CA 510 CA 0 CA Firing order: 1-3-4-2 Compression ratio 20.36:1 Displacement Stroke 449.77 cc 88.90 mm Connecting rod mm 158.0 Valve timings: IVO IVC EVO EVC +352 after TDCa 138 after TDCa +120 after TDCa 348 after TDCa a Crank angle degree after firing TDC. Table A3. Properties of natural gas in Thailand (2010) Lower heating valve, MJ/kg 34.34 Stoichiometric A/F (without 16.29 CO 2 and N 2) Methane, % by mole 74.8 Ethane, % by mole 6.3 Propane, % by mole 2.0 i-propane, % by mole 0.4 n-butane, % by mole 0.4 Larger hydrocarbon (> C 6), % 0.1 by mole CO 2, % by mole 13.8 N 2, % by mole 2.2 Table A2. Ricardo Hydra engine specifications Engine Type 2-Valve DI Diesel Ricardo Hydra Fuel system Common-rail Aspiration Naturally aspirated