Hydrogen fuelled agricultural diesel engine with electronically controlled timed manifold induction: an experimental approach

Energy and Sustainability II 103 Hydrogen fuelled agricultural diesel engine with electronically controlled timed manifold induction: an experimental approach P. K. Bose 1, S. Mitra 2, R. Banerjee 3, D. Maji 3 & P. Bardhan 4 1 National Institute of Technology, Silchar, India 2 Jalpaiguri Engineering College, India 3 School Of Automotive Engineering, Jadavpur University, India 4 JIS College of Engineering, India Abstract The important motivations for exploring alternative fuel resources are energy security, air pollution, and climate change; problems that are collectively calling into question the fundamental sustainability of the current energy system. Natural gas and bio fuels are seen as the most important short-term options for meeting these goals, whereas in the long run, a substantial contribution is expected to be delivered by hydrogen which would facilitate the transition from limited non-renewable stocks of fossil fuels to unlimited flows of renewable sources. Hydrogen-fuelled internal combustion engines with near-zero emissions and efficiencies exceeding today's port-fuel-injected (PFI) engines are a potential near-term option and a bridge to hydrogen fuel cell vehicles where fuel cell undergoes development to make it economically viable. The unique combustion properties of hydrogen make it an ideal choice for its use in compression ignition engines. The present work attempts to explore the performance and emission characteristics of an existing single cylinder four-stroke compression ignition engine operated in dual fuel mode with hydrogen as an alternative fuel. The hydrogen was premixed with the incoming air and inducted during the duration of intake valve opening by an indigenously developed electro-mechanical means of solenoid actuation The performance and emission characteristics with hydrogen diesel blend and neat diesel are compared. In this experiment hydrogen flow rate was kept constant at 0.15 kg/hr. The brake thermal efficiency with hydrogen diesel blend is about 15.7% greater than that of neat diesel operation at 40% rated load. CO, CO 2, HC and smoke emissions were significantly less with hydrogen diesel blend. Smoke level was 41.6% lower than that of neat diesel operation at 80% load, whereas emission of CO 2, CO, and HC levels were lower by 40.5%, 44.3% and 53.2% respectively for hydrogen enrichment at 80% load. In our present work EGR technique was examined in reducing NOx concentration. The NOx level decreased from 1211 ppm to 710 for hydrogen enrichment (0.15kg/hr) at 80% of the rated load. Keywords: hydrogen, diesel, dual-fuel, timed manifold injection, electromechanical actuation, hot EGR, cold EGR. doi:10.2495/esu090101

104 Energy and Sustainability II 1 Introduction With the uncertainty of today's petroleum market with its declining oil reserves, ongoing tensions in oil producing nations, and environmental regulatory activity soaring to new heights, the time has come for the world to embark on the road of independence from the addiction of fossil fuel and to find sustainable alternative fuel resources of the future. According to the European Commission s White Paper European transport policy for 2010: time to decide, natural gas and bio fuels are seen as the most important short-term options for meeting these goals, whereas in the long run, a substantial contribution is expected to be delivered by hydrogen which would facilitate the transition from limited nonrenewable stocks of fossil fuels to unlimited flows of renewable sources. According to the World Energy Assessment, released in 2000 by several UN agencies and the World Energy Council, which emphasizes the strategic importance of hydrogen as an energy carrier, the accelerated replacement of oil and other fossil fuels with hydrogen could help achieve deep reductions in carbon emissions and avoid a doubling of pre-industrial carbon dioxide (CO 2 ) concentrations in the atmosphere a level at which scientists expect major, and potentially irreversible, ecological and economic disruptions. Hydrogen-fuelled internal combustion engines with near-zero emissions and efficiencies exceeding today's port-fuel-injected (PFI) engines are a potential near-term option and a bridge to hydrogen fuel cell vehicles where fuel cell undergoes developments to make it economically viable (Is Hydrogen the Solution? [1]). Under the given circumstances, dual fuel operation with hydrogen within the framework of contemporary existing engine structure is a good alternative. The high flame speed of hydrogen makes engine operation approach the ideal Otto cycle with near constant volume heat addition thus enhancing thermal efficiency. In addition, the potential of hydrogen combustion in reducing green house hydrocarbon, smoke and PM emissions provide the motivation of study of a hydrogen fuelled diesel engine combining both the advantages of a spark ignition engine and a compression ignition engine at the same time. 1.1 Hydrogen as an alternative fuel in compression ignition engines The use of hydrogen as a clean fuel for premixed spark ignited engines is fairly well developed, (Yi et al. [2], Das et al. [3], Das [4], El-Emam and Desoky [5], Karim [6], Subba Rao et al. [7]) but the same is not true for use in diesel engines. However, the unique combustion properties of hydrogen make it an ideal choice for its use in compression ignition engine. The burning velocities of hydrogen air mixture range from 153 to 232 cm/sec for its stoichiometric mixture, (Isadore and Drell [8], Wallace and Ward [9]). This results in a more isochoric, thus thermodynamically more favourable combustion than conventional diesel engines which undergo a pressure and temperature rise spread over several degrees of crank travel. The flammable range is exceptionally wide for hydrogen in air-lower limit 4%, upper limit 75% by volume. (Isadore and Drell [8], Wallace and Ward [9]) This is an equivalence ratio of about 0.24, as compared with a lean flammability limit of about Φ=0.5 for most hydrocarbon fuels.

Energy and Sustainability II 105 A significant advantage is that the engine can work with very lean mixtures, thus omitting a throttle valve this ideally suits a diesel engine operation. Hydrogen has a higher auto ignition temperature than conventional fossil fuels. This means that a higher compression ratio is allowed than in a gasoline engine and this makes it an ideal candidate for use in high compression ratio engines without any danger of knocking. 1.2 The hydrogen -diesel dual fuel concept The hydrogen-diesel dual fuel concept method combines the advantages of the high part load efficiency, lower specific fuel consumption, of a diesel engine and the clean combustion characteristics of hydrogen and oxygen. However hydrogen with its cetane number being very low, are not directly suited to compression-ignition (CI) engines. Hydrogen has an auto-ignition temperature of about 571 C and as such it is not possible to achieve ignition of hydrogen by compression alone at the compression ratio of 17.5 at the existing engine configuration in the present work. Some source of ignition has to be created inside the combustion chamber to ensure ignition. (Ikegami et al. [10], Lee et al. [11], Mansour et al. [12], Naber and Siebers [13]). A small amount of liquid Diesel fuel is injected by means of the existing fuel injection equipment near the end of the compression stroke to ignite the gaseous mixture. Diesel fuel auto ignites and creates ignition sources for the surrounding air gaseous fuel mixture. The pilot liquid fuel, which is injected by the conventional diesel injection equipment, normally contributes only a small fraction of the engine power output. In dual-fuel engines both types of combustion coexist together the primary gaseous fuel of high-octane index is premixed with air in the inlet manifold and compressed and then fired by a small liquid fuel injection which ignites spontaneously at the end of compression phase. The advantage of this type of engine resides in the fact that it is an attempt for the combination of the better of the two combustion processes using the difference of flammability of two fuels at different stages of the combustion process. 2 Hydrogen induction: some considerations Hydrogen is a peculiar fuel and it has properties distinct from the conventional fossil fuels. (El-Emam and Desoky [5], Isadore and Drell [8], Wallace and Ward [9]) The necessary ignition energy of a hydrogen-air mixture is very low (0.02 mj), especially at the stoichiometric condition. This enables the ignition of very lean mixtures and ensures immediate ignition. Contact with hot spots or residual gas, can cause the mixture to ignite spontaneously. (Liu and Karim [14]) This pre-ignition tendency results in backfire if the mixture ignites when the inlet valve is still open. The flame in the combustion chamber ignites the mixture in the inlet manifold through the inlet port, which causes a very loud bang and can result in severe engine damage. The backfire phenomenon is also called flashback or back flash and is one of the main issues of hydrogen fuelled internal combustion engines. Hydrogen has a small quenching distance, about three times as small as gasoline. This implies that it can burn slowly in small and narrow

106 Energy and Sustainability II clearances, like crevice regions. The burning in these small regions can continue up to and during the intake process. During the intake process, the hot burning gases can flow out of the crevice volumes and ignite the intake charge thus causing backfire. Thus if an existing IC engine without any modification were to be fuelled by hydrogen, some problems, such as small power output, abnormal combustion (e.g. backfire, pre-ignition, high pressure rise rate and even knock) would occur. So its fuel supply system and combustion system need suitable modification. The prevalent modes of hydrogen induction were examined and their merits and demerits were evaluated in the present context on the basis of literature survey (Yi et al. [2], Das et al. [3], Das [15], Lee et al. [11], Zhenzhong et al. [16], HariGanesh et al. [17], Varde and Frame [18]) Timed manifold injection (TMI) systems offer an alternative to load control method by throttling. It possesses the ability to initiate fuel delivery at a timing position sometimes after the beginning of intake stroke ensuring a pre-cooling effect and thus rendering the pre-ignition sources ineffective. Furthermore, it helps to quench and dilute any residual combustion products that could be present in the compression space near TDC. 2.1 Hydrogen induction circuit development The design of the solenoid actuation [Fig1], which formed the heart of the TMI system, was dictated by the necessity of ensuring simplicity in implementation and the reduction of possibility of undesirable effects of abnormal hydrogen combustion such as pre ignition and flashback at the operating loads. The triggering mechanism essentially consisted of a metal plate mounted on a damper spring held in place by an actuator mounting as shown in Fig 1. The metal plate was designed to ensure a positive contact with the free end of the rocker arm during the inlet valve opening. The design ensured a contact only during the maximum valve lift. The contact having made, the metal plate acting as the switch, closed the 12V DC circuit, thereby energizing the solenoid and allowing hydrogen gas to be injected at a predefined rate in the inlet manifold The metal plate lost contact with the rocker arm during the closing of the inlet valve ensuring that hydrogen being injected into the cylinder only during the maximum valve lift as dictated by the dwell period of the valve lift cam and also that hydrogen was inducted only after a definite time lag after the initiation of the opening of the inlet valve. The time lag arising out of mechanical inertia of the valve components ensured that hydrogen was injected only after a sufficient flow of cooler ambient air was inducted in the cylinder during the opening of the inlet valve, this being critical in quenching any residual hot spots remaining in the cylinder thereby removing any possibility of flash back.in the present study, the hydrogen gas was routed to the engine. According to the setup shown in Fig 2. The hydrogen induction inside the cylinder being actuated by a solenoid is periodic in nature rather than continuous. As a result, a surge tank is included in the circuit to dampen out any pressure fluctuations in the hydrogen supply line. A flow regulator in the hydrogen circuit was used to regulate the mass flow rate of hydrogen in the hydrogen circuit. A flame trap was incorporated in the setup keeping in mind the inherent explosive nature of a hydrogen air mixture and the

Energy and Sustainability II 107 Figure 1: Solenoid actuated electro-mechanical TMI circuit. Figure 2: Schematic diagram of experimental setup. flashback and blow off nature of hydrogen flames. This acts a safety buffer against explosive mixtures formed in the intake manifold to travel back to the hydrogen cylinder by quenching any freak flame. 3 Methodology The diesel engine was fired on no load initially and it was run for a period of time until it reached steady state conditions, denoted by the constant cooling water outlet temperature. Then the engine running on diesel as the main fuel was taken on load in steps by means of the Eddy current dynamometer of SAJ TEST PLANTS make and after attaining the steady-state conditions all the pertinent readings were noted. This procedure was repeated for 20%, 40%, 60% and 80% loading. The engine exhaust was analysed by means of a AVL 437 smoke meter while common engine emissions (CO,HC,CO2,O2,NOX) were calculated via a

108 Energy and Sustainability II AVL DIGAS 444-5 gas analyzer fitted with a DIGAS SAMPLER. The engine was again allowed to attain steady state conditions at no load. Then hydrogen was supplied at a pressure of 1 bar using hydrogen pressure regulator. By keeping the flow of hydrogen gas@ 0.15kg/hr, the performance and emissions of the hydrogen enriched engine without EGR were noted at 20%, 40%, 60% and 80% load. At the end of this process, hydrogen flow rate was reduced to zero and the engine was made to run at steady-state condition using diesel at no load condition. For EGR operation the quantity of exhaust gas was regulated by a control valve [Fig 3], installed in the EGR loop. An air box was provided in EGR loop to dampen the fluctuation of recirculated exhaust. An orifice was installed in the EGR loop after the air box in order to measure the flow rate of recirculated exhaust. There was an EGR cooler placed before the air box. The engine was run by using hydrogen enrichment (0.15kg/hr hydrogen flow) with 10% EGR and 20% EGR in hot and cold conditions. In both these cases above mentioned readings are taken on no load, 20% load, 40% load, 60% load and 80% load. Figure 3: EGR setup. 4 Results and discussions 4.1 Performance characteristics 4.1.1 Variation of brake thermal efficiency with brake power The variation of brake thermal efficiency with brake power is shown in Fig 4. The brake thermal efficiency for hydrogen with diesel as ignition source is 34.1% at 80% load with a flow rate of hydrogen 0.15kg/hr whereas that of baseline diesel fuel is 30.2% showing an appreciable increase of 12.9%. This increase in thermal efficiency is attributed to an enhanced combustion rate due to high flame velocity of hydrogen. Use of EGR has a negative effect on engine combustion due to fresh air dilution and addition of inert elements such that efficiency decreases for all cases of EGR operation as compared to hydrogen enrichment but is greater at all loads when compared with neat diesel operation. At 80% load with 10% cold EGR brake thermal efficiency is 32.3% and with 10% hot EGR it is 32.45% while that for 20% cold EGR is 30.8%, thus indicating that thermal efficiency under the present conditions was affected by the quantity and quality (hot or cold) of EGR operation.

Energy and Sustainability II 109 Figure 4: Variation of brake thermal efficiency with load. 4.1.2 Variation of brake specific fuel consumption with brake power Fig 5 shows the variation of brake specific fuel consumption with brake power Part load operation (20% load) shows a drastic reduction of 63.3% in bsfc readings during hydrogen enrichment as compared with neat diesel operation proving the excellent combustion properties of hydrogen which helps to achieve the desire brake power at a lower energy input. All EGR cases of operation showed a reduced trend of bsfc while 10% hot EGR showed the best characteristics when compared to pure diesel operation with a 61.71% and 43.3% reduction in bsfc readings at 20% and 80% load. 4.1.3 Variation of volumetric efficiency with brake power The air/fuel ratio (A/F ratio) of stoichiometric combustion of hydrogen in air based on mass is 34.33 kg air/kg and that based on volumetric analysis is 29.6% Volume percent of the combustion chamber occupied by hydrogen is then 29.6%. This means that a significant part of a given combustion chamber volume cannot be filled with air in contrast with conventional liquid fuel that only displaces 1.8% of the combustion chamber. Figure 5: Variation of BSFC with load.

110 Energy and Sustainability II Figure 6: Variation of volumetric efficiency with load. This decreases the volumetric efficiency of a given engine when compared to its operation with conventional liquid fossil fuel. Fig 6 shows the variation of volumetric efficiency with brake power. The volumetric efficiency obtained for 0.15kg/hr hydrogen enrichment without EGR is 78.9% compared to neat diesel fuel of 80.1% at 80% load. Volumetric efficiency decreases with all cases of EGR operation. Maximum penalty is suffered during 20% hot EGR operation with a 50.1% efficiency at 80% load.10% cool EGR provided the best volumetric efficiency characteristics among all EGR operations with 70.2% at no load and 63.9% at 80% load. 4.2 Emission characteristics 4.2.1 Carbon dioxide emissions The variation of CO 2 emission with brake power for all cases under study is shown in Fig 7. CO 2 emissions in case of hydrogen enrichment are lower compared to that of diesel. At 80% load CO 2 emission for hydrogen enrichment without EGR is 4.7% by volume where as that of neat diesel is 7.9% by volume. The CO 2 emission in case of hydrogen enrichment is lowered because of better combustion characteristics of hydrogen fuel and also due to the absence of carbon atom in hydrogen molecule. Due to the use of EGR, CO 2 emissions increase and go on increasing with the increase in EGR percentage. At 80% load CO 2 emission for 10% EGR is 4.8% by volume and that of 20% EGR is 5.6% by volume. The reason of this increase in CO 2 emissions in case of EGR is the presence of CO 2 in exhaust gas being recycled back to the fresh air intake. 4.2.2 Carbon monoxide emissions Fig 8 depicts the variation of carbon monoxide with brake power. Results indicate a drastic reduction of 86.6% as compared to neat diesel operation at no load for hydrogen enrichment while 45.8% reductions at 80% load for the same conditions. Hydrogen does not contain any carbon. This is the reason for low CO emission in case of hydrogen enrichment, and the registered amount being only due to pilot diesel and lube oil. Operation with EGR resulted in reduction of CO

Energy and Sustainability II 111 Figure 7: Variation of CO 2 emissions with load. Figure 8: Variation of carbon monoxide emissions with load. emissions for all cases as compared to pure diesel operation but had a reduced gain as compared to hydrogen enrichment. Operation under 10% hot EGR produced the best gains in CO emissions among all EGR operations with a reduction of 42.3% at 80% load as compared to neat diesel operation. Further analysis showed that gains in CO emission reduction reduced with increasing load for all cases of dual fuel operation. 4.2.3 Hydro carbon emissions Fig 9 shows the variation of HC with brake power.it can be observed that HC emission for hydrogen enrichment without EGR scores an 83% reduction compared to neat diesel operation at no load and a 57% reduction at 80% load. The best HC reduction characteristics in EGR operations were provided by 10% hot EGR with a 57.6% reduction at 80% load. Diesel engines with their inherent lean combustion are prone to HC emissions due to inhomogeneous local air fuel ratios which are either over lean or fuel rich to support combustion. The interesting observation with dual fuel operation with hydrogen is that though the overall equivalence ratio of the combustible mixture is leaner than that of normal

112 Energy and Sustainability II diesel operation the HC emissions are still remarkably lower. This is attributed to a more homogenous air fuel mixture having wide ignitability limits due to hydrogen, which helps sustain combustion even under lean conditions. The gains in mixture quality are penalized with EGR operation where residual gases promote fresh air dilution and increases local equivalence ratios beyond ignitability limits. Figure 9: Variation of HC emissions with load. 4.2.4 Smoke emissions The operation range of diesel engines is mainly constrained by the smoke emissions at high loads. This limits the exploitation of the advantages of a compression ignition engine to its fullest potential. The variation of smoke level with brake power is shown in Fig 10. As the load increases, diesel engines tend to generate more smoke. Present analysis showed that gains in smoke reduction were maximum with hydrogen enrichment for all the load ranges but decreasing with increasing load, with a maximum of 64.28% at 40% load and a notable 41.6% at 80% load.egr operation registered lesser gains in smoke reduction as Figure 10: Variation of smoke emissions with load.

Energy and Sustainability II 113 compared to hydrogen enrichment, the 10% hot EGR case showing the best gain trend among all EGR operations. Hydrogen being devoid of any carbon atoms show obvious characteristics of reduction in smoke levels. This is why there is low smoke level in case of hydrogen enrichment. Smoke level increases with increasing EGR rate and increasing engine load. EGR reduces availability of oxygen for combustion of fuel which results is relatively incomplete combustion and increased formation of particulate matter. This results in higher smoke level in case of EGR. 4.3 NO x emissions Fig 11 shows the variation of NO x with brake power. NO x emission for hydrogen enrichment without EGR is 1211 ppm compared to neat diesel fuel of 810 ppm at 80% load. The reason for this higher concentration of NO x in case of hydrogen enrichment without EGR is peak combustion temperature and high residence time of the high temperature gases in the cylinder. Fig 11depicts that with 10% EGR, NOx formation is 760 ppm at 80% load and that of 20% EGR is 710ppm. So the NO x formation decreases with the use of EGR and goes on decreasing with increase in EGR percentage. The primary effect of the burned gas diluents in the unburned mixture on the NOx formation process is that it reduces peak temperatures by increasing the heat capacity of the cylinder charge, per unit mass of fuel. When recirculated to engine inlet, it reduces oxygen concentration and act as a heat sink. All the combustion process is delayed with diluted air consequently the whole combustion process is shifted further into the expansion stroke, leading to lower combustion temp. Lower combustion temp is the reason of decrease of NO x. Figure 11: Variation of NO x emissions with load. 5 Conclusion The present study showed a persistent increase of the brake thermal efficiency over the entire range of operation under all cases of hydrogen enrichment with a maximum increase of 15.73% at 40% load.the bsfc decreased with all cases of

114 Energy and Sustainability II hydrogen enrichment (with and without EGR) showing a significant decrease of 63.3% at 20% load. The volumetric efficiency suffers a decrease for all cases of hydrogen enrichment with a decrease of 37.5% at 80% load. Smoke emissions displayed a decrease for all cases of hydrogen enrichment with a decrease of 64.28% and 61.5 at 20% and 40% load respectively for non EGR cases, thereby improving the part load operation characteristics. HC emissions decreased for the entire range of operation for hydrogen enrichment with a substantial decrease of 80.0% at 20% load and a 57.6% decrease at 80% load. CO emissions reduced remarkably by 69.5% and 64.5% at 20% and 40% loading with a trend of decrease for all hydrogen enrichment operations as compared with neat diesel combustion. Hydrogen enrichment as compared to pure diesel operation displayed a steady decrease of CO 2 for all ranges of operation with a decrease of 71.05% and 40.05% at 20% and 80% loading. The ultra-lean combustion characteristics of hydrogen provide the perfect environment for NOx emissions which are compounded with the inherent tendency of neat diesel fuel combustion. It thus creates a challenge to solve the paradox of simultaneously reducing NOx emissions and simultaneously reap the benefits of using hydrogen in the context of reduced pollutant emissions of typical diesel engines. In our present work EGR technique was examined in reducing NOx concentration. The NOx level decreased from 1211 ppm to 710 for hydrogen enrichment (0.15kg/hr) at 80% of the rated load. NOx levels showed a decreasing tendency for all EGR induction under these conditions of hydrogen enrichment. The emergence of hydrogen as a sustainable fuel for the future is well established by now. Its pertinence to internal combustion engines which still must be considered the best driving units of the immediate future dictates the exploration of hydrogen as a strategic sustainable energy carrier for internal combustion engines. In view of this, the present study offers a pilot study to extend the operational benefits of using hydrogen in compression ignition engines which form the mainstay of the present industrial powerhouse. References [1] Hydrogen the Solution? http://www.nrdc.org/air/transportation/ phydrofuel.asp [2] H.S. Yi, K. Min and E.S. Kim. The Optimised Mixture Formation for Hydrogen Fuelled Engines. International Journal of Hydrogen Energy 25(7) pp: 685-690. 2000. [3] L.M. Das, Rohit Gulati and P.K. Gupta (June 2000). Performance Evaluation Of A Hydrogen-Fuelled Spark Ignition Engine Using Electronically Controlled Solenoid-Actuated Injection System. International Journal of Hydrogen Energy 25(6) pp: 569-579; 2000 [4] Das, L. M. Hydrogen engine: research and development (R&D) programmes in Indian Institute of Technology (IIT), Delhi International Journal of Hydrogen Energy 27(9) pp: 953-965; 2002 [5] El-Emam, S. H. and A. A. Desoky (1985). A study on the combustion of alternative fuels in spark-ignition engines. International Journal of Hydrogen Energy 10(7-8): 497-504.

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