HYDROGEN FUELLED IC ENGINE AN OVERVIEW VVN BHASKAR Associate Professor, Dept. of ME, ACE, Madanapalle,A.P,India.

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1 HYDROGEN FUELLED IC ENGINE AN OVERVIEW VVN BHASKAR Associate Professor, Dept. of ME, ACE, Madanapalle,A.P,India. Dr. R. HARI PRAKASH Principal, Brahmaiaha College of Engineering, Nellore, A.P, India Dr. B. DURGA PRASAD Associate Professor, Dept of ME, JNTUCE, Anantapur, A.P, India Abstract- Hydrogen as a fuel in Internal Combustion engines is a solution for the near future to realize zero CO emissions for traffic applications. The hydrogen fuelled IC engine is ready for that. The storage and production of hydrogen, and to build the necessary infrastructure, are the real shortcomings in the general use of hydrogen in IC engines. This paper gives an overview of the development of hydrogen fuelled IC engines by the most important car manufactures (Ford, BMW etc.). This overview indicates the evolution in the development of hydrogen fuelled engines (different generation of engines). This evolution is also made at Ghent University. Ghent University has been working for nearly 15 years on the development and optimization of hydrogen engines. Several test rigs are in function (all with electronic control management systems and sequential multi-point injection). Keywords - IC engines; hydrogen; emissions; backfire I. II. HYDROGEN IC ENGINES FOUR GENERATIONS INTRODUCTION The incentives for a hydrogen economy are the emissions, the potentially CO -free use, the sustainability and the energy security. In this paper the focus is on the use of hydrogen in internal combustion engines (ICE), or more precisely, hydrogen fuelled spark ignition (SI) engines. When talking about hydrogen as a fuel for traffic applications, most people make the link to fuel cells. Why? Why not a more realistic link to internal combustion engines? At the moment the estimation of the number of motor vehicles is about 800 million. To replace them in a relatively short time by fuel cells is impossible. There are several reasons for converting the gasoline, diesel or natural gas engines to hydrogen fuelled internal combustion engines. ICEs are proven technology, are simple and well-known and the adaptations can be made with a low cost. During the transition period bi-fuel solutions are possible (to run the engine either on gasoline or pure hydrogen). For larger engines (buses, trucks) mixtures of natural gas with hydrogen (about 0%) are easy to exploit. During this transition period, experience can be gained with the production, storage and infrastructure of hydrogen. Currently the hydrogen production is the cheapest through the steam reforming of methane, but CO emissions cannot be avoided. Renewable energy, e.g. solar power, hydroelectric, tidal etc., can give CO -free electricity to electrolyze water to hydrogen. The downside is that these electricity costs are mostly expensive. Interesting is also the application of peak shaving of wind turbine power. Other possibilities are solar thermal, biomass, bacterial etc. Several solutions are possible for the hydrogen storage. Liquid storage gives a high mass density but asks a high energy demand. Mostly used is the compressed storage, vessels with a compression pressure of 350 bar are homologated and up to 700 bar are demonstrated. There are four generations in the development of hydrogen fuelled engines. In the first generation a gas venturi is used. With a gas carburetor a large volume of combustible mixture is in the inlet manifold. To avoid backfire (an explosion in the inlet manifold before the inlet valve closes), the engine has to run lean (λ ) which results in a low power output. For the second generation the same technologies are used as for gasoline SI engines: multipoint sequential (port) injection and electronic engine control. A possible strategy is then to use a late injection so that the admitted air will cool the inlet manifold and the combustion chamber before the injection of hydrogen. These injectors are now currently commercially on the market (after a delay of introduction due to the high volume of a low density gas to inject in a short time). Even with a late injection a stoichiometric mixture (λ = 1) is not always possible and the power output is lower than a corresponding gasoline engine, see e.g. Ford s results reported by Tang et al. (00). For the third generation, at high loads, the mixture is kept stoichiometric (λ = 1). To avoid backfire, exhaust gas recirculation (EGR) is used. At this stoichiometric mixture a three way catalyst (TWC) can be used to decrease the NOx emissions. And with turbo/supercharging and inter cooling the same or a higher power output is obtained as for a gasoline engine, as demonstrated by BMW obtaining an indicated mean effective pressure (imep) of 18 bar Berckmüller et al. (003), and Ford reaching gasoline engine torque outputs with a boost pressure of 1.85 bar Natkin et al. (003). Finally for the fourth generation, research is going on into direct injection of hydrogen in SI engines, e.g. by BMW Gerbig et al. (004), Rottengruber et al. (004). III. EXPERIMENTAL REVIEW RESEARCH: LITERATURE Page 46

2 Here, an overview is given of the design features in which a dedicated hydrogen engine differs from traditionally fuelled engines, following Verhelst (005). A. Abnormal combustion The suppression of abnormal combustion in hydrogen engines has proven to be quite a challenge and measures taken to avoid abnormal combustion have important implications for engine design, mixture formation and load control. For sparkignition engines, three regimes of abnormal combustion exist: knock (auto-ignition of the end gas region), pre-ignition (uncontrolled ignition induced by a hot spot, premature to the spark ignition) and backfire (also referred to as backflash, flashback and induction ignition, this is a premature ignition during the intake stroke, which could be seen as an early form of pre-ignition). Backfire has been a particularly tenacious obstacle to the development of hydrogen engines. The causes cited for backfire are: Hot spots in the combustion chamber: deposits and particulates - Bardon and Haycock (00), MacCarley (1981); the spark plug Das (00), Lucas and Morris (1980); residual gas - Das (1996), Lucas and Morris (1980), Berckmüller et al. (003); exhaust valves Berckmüller et al. (003), Stockhausen et al. (00), Swain et al. (1988), TÜV Rheinland (1990) ; etc. Residual energy in the ignition circuit - Lucas and Morris (1980), Kondo et al. (1997) Induction in the ignition cable - MacCarley (1981) Combustion in the piston top land persisting up to inlet valve opening time and igniting the fresh charge Lucas and Morris (1980), Swain et al. (1996), Koyanagi et al. (1994), Lee et al. (000) Pre-ignition - Tang et al. (00), MacCarley (1981), Swain et al. (1988), Koyanagi et al. (1994), Lee et al. (1995) All causes itemized above can result in backfire and the design of a hydrogen engine should try to avoid them, as engine conditions different from normal operation are always a possibility. B. Air- Fuel Mixture formation A range of mixture formation methods has been tested for hydrogen engines, mostly in the pursuit of backfire-free operation: External mixture formation with a gas carburetor Lucas and Morris (1980), Jing-Ding et al. (1986) External mixture formation with `parallel induction', that is: some means of delaying the introduction of hydrogen, e.g. a fuel line closed by a separate valve on top of the intake valve that only opens when the intake valve has lifted enough Olavson et al. (1984) External mixture formation with a gas carburetor and water injection - TÜV Rheinland (1990), Binder and Withalm (198), sometimes with additional exhaust gas recirculation (EGR) Davidson et al. (1986) External mixture formation with timed manifold or port fuel injection (PFI) - Tang et al. (00), MacCarley (1981), Berckmüller et al. (003), Swain et al. (1996), Lee et al. (1995), Natkin et al. (003), Heffel et al. (1998), sometimes also with some means of parallel induction Heffel et al. (001) Internal mixture formation through direct injection (DI) Meier et al. (1994), Furuhama (1997), Guo et al. (1999), Kim et al. (1995) During the last decade, only timed port injection and direct injection (during the compression stroke or later) have been used, as the other methods are less flexible and less controllable. External mixture formation by means of port fuel injection has been demonstrated to result in higher engine efficiencies, extended lean operation, lower cyclic variation and lower NOx production compared to direct injection Smith et al. (1995), Yi et al. (000). An important advantage of DI over PFI is the impossibility of backfire. This too increases the maximum power output of DI compared to PFI as richer mixtures can be used without fear of backfire. Pre-ignition can still occur though, unless very late injection is used. C. Load control strategies Hydrogen is a very versatile fuel when it comes to load control. The high flame speeds of hydrogen mixtures and its wide flammability limits permit very lean operation and substantial dilution. The engine efficiency and the emission of NOx are the two main parameters used to decide the load control strategy. Constant equivalence ratio throttled operation has been used but mainly for demonstration purposes Olavson et al. (1984), Davidson et al. (1986), as it is fairly easy to run a lean burn throttled hydrogen engine (accepting the severe power output penalty). Where possible, wide open throttle (WOT) operation is used to take advantage of the associated increase in engine efficiency Heffel et al. (001), Smith et al. (1995), so regulating load with mixture richness (qualitative control) instead of volumetric efficiency (quantitative control) and thus avoiding pumping losses. Across the load range of the engine, different strategies, which try to make as much advantage as possible of the properties of the hydrogen-air mixture, can be used. It is important to know that NOx production is very dependent on the mixture richness, the air-to-fuel equivalence ratio λ, as this is the major parameter controlling the maximum combustion temperature. At lean mixtures NOx production is very low until a certain λ is reached, the so-called NOx formation limit. A mixture richer than this limit, which is normally around λ =, will produce high levels of NOx and a maximum will be reached at about λ = 1.3. So, for loads below this NOx formation limit, a quality-based mixture control will be used. For idling and very low loads the mixture has to be very lean Page 47

3 with WOT (λ > 4). At these lean mixtures the coefficient of variation for imep (COV) is high due to the lower combustion velocity and combustion stability. Therefore throttle control, in order to enrich the mixture, is used at these loads. High efficiencies of more then 40% are reported in this operating range Berckmüller et al. (003). Depending on the mixture formation, different methods can be use to control the engine at high loads. Beyond the NOx formation limit throttled stoichiometric operation with a reduction catalyst can be used, as demonstrated by BMW Rottengruber et al. (004). This catalyst for NOx reduction can be used with great efficiency (> 99.5%), because H, which is present in the exhaust feed gas at λ = 1, is a highly efficient reducing agent. For higher efficiency, EGR (0 50%) instead of throttling can be used in this load range to control the amount of fresh air in the engine, this has been reported by Ford Natkin et al. (003). Efficiencies of 35% and 40% are reported for respectively throttle and EGR control in this load range. If the engine is charged, for loads above the naturally aspirated full load limit, control is possible by regulating the charge pressure while keeping a stoichiometric mixture. Another strategy proposed by BMW is to use the common port injection for low and part load, and direct injection for high loads Rottengruber et al. (004). External mixture formation is advantageous because of the better mixture preparation (mixing) and less throttling requirements due to the lower volumetric efficiency. NOx emissions of less than 1 ppm are reported with the use of a normal three way catalyst in stoichiometric operation Natkin et al. (003). If a hydrogen engine is designed for single speed/power operation, e.g. for stationary power generation or for a series hybrid vehicle, very clean and highly efficient operation is possible without any after treatment (of which the effectiveness could deteriorate with time). NOx emissions below 10 ppm or even 1 ppm, with indicated efficiencies of perhaps 50 % are possible - Smith et al. (1995), Van Blarigan (1996), Aceves and Smith (1997). Hydrogen is the only fuel with which this is possible (with hydrocarbons, decreasing NOx emission with lean burn implies increased unburned hydrocarbon emissions). D. Hydrogen SI engines Here, an attempt is made to provide a comprehensive overview of engine design features that make the most of hydrogen's advantages and counter its disadvantages. Spark plugs: use cold rated spark plugs to avoid spark plug electrode temperatures exceeding the autoignition limit and causing backfire Das (00), Kondo et al. (1997). Ignition system: avoid uncontrolled ignition due to residual ignition energy by properly grounding the ignition system or changing the ignition cable's electrical resistance - TÜV Rheinland (1990), Kondo et al. (1997). Injection system: provide a timed injection, either using port injection and programming the injection timing such that an initial air cooling period is created in the initial phase of the intake stroke and the end of injection is such that all hydrogen is inducted, leaving no hydrogen in the manifold when the intake valve closes; or using direct injection during the compression stroke. Hot spots: avoid hot spots in the combustion chamber that could initiate pre-ignition or backfire, use cooled exhaust valves; use multi-valve engine heads to further lower the exhaust valve temperature Stockhausen et al. (00), Swain et al. (1988), TÜV Rheinland (1990). Piston rings and crevice volumes: decrease the piston top land clearance to prevent hydrogen flames from propagating into the top land. Valve seats and injectors: the very low lubricity of hydrogen has to be taken into account, suitable valve seat materials have to be chosen Stockhausen et al. (00), TÜV Rheinland (1990), and the design of the injectors should take this into account. Lubrication: an engine lubrication oil compatible with increased water concentration in the crankcase has to be chosen. Crankcase ventilation: positive crankcase ventilation is generally recommended due to unthrottled operation (high manifold air pressures) and to decrease hydrogen concentrations (from blowby) in the crankcase - Stockhausen et al. (00), Strebig and Waytulonis (1987). Compression ratio: this should be chosen as high as possible to increase engine efficiency, with the limit given by increased heat losses or appearance of abnormal combustion (in the case of hydrogen primarily pre-ignition). In-cylinder turbulence: because of the high flame speeds of hydrogen, low turbulence combustion chambers (pancake or disk chamber and axially aligned symmetric intake port) can be used which are beneficial for the engine efficiency Swain et al. (1988), Swain et al. (1996), Van Blarigan (1996). Electronic throttle: as stated above, hydrogen engines should be operated at wide open throttle wherever possible, but throttling is needed at very low loads to maintain combustion stability and limit unburned hydrogen emissions. At medium to high loads, throttling might be necessary to limit NOx emissions. This can only be realized with a drive-by-wire system. Page 48

4 IV. ADVANTAGES OF HYDROGEN FOR SPARK IGNITION ENGINES Fig 1: Flammability limits for air with hydrogen (H ), air with natural gas (CH ) and air with gasoline 4 Fig. 1 gives the flammability limits for different fuels at normal temperature and pressure. As can be seen the flammability limits (= possible mixture compositions for ignition and flame propagation) are very wide for hydrogen (between 4 and 75% hydrogen in the mixture) compared to gasoline (between 1 and 7.6%). This means that the load of the engine can be controlled by the air to fuel ratio, as for diesel engines. Nearly all the time the engine can be run with a wide open throttle, resulting in a higher efficiency. The second advantage of hydrogen for SI engines is the high burning velocity. For nearstoichiometric mixtures (near λ = 1/ φ = 1) the combustion is almost a constant-volume combustion, which increases the (thermodynamic) efficiency. Also the properties of lean hydrogen flames will cause flame acceleration due to cellularity and no turbulence enhancing methods have to be used (swirl ports, etc.). Again this increases the efficiency of the engine. Furthermore, hydrogen has a high octane number and the compression ratio of the engine can be increased. This, of course, increases the efficiency. Finally the emissions of a hydrogen engine are very clean, only the noxious component NOx is emitted. The very first work done was basically a proof of concept. Simply put, a direct injection diesel engine was taken (Valmet inline four, 4.4 liter), the diesel fuel injectors were replaced by spark plugs, the compression ratio was lowered (from 16:1 to 8.7:1) by installing different pistons and a gas carburetor was mounted Sierens (199). The influence of engine parameters on the combustion of hydrogen was studied using heat release analysis of cylinder pressure measurements Sierens and Rosseel (1996). The study of the cylinder pressure prior and during the occurrence of backfire showed a runaway pre-ignition to lead to backfire - Sierens and Rosseel (1998). The pre-ignition was mostly accompanied by engine knock and a knock detection algorithm based on cylinder pressure data was proposed to avoid knock and backfire Rosseel and Sierens (1997). The gas carburetor was eventually replaced by a sequential injection system, involving the testing of gas injectors for hydrogen (at the time not commercially available and unreliable) Sierens and Rosseel (1995). Fig : Power output of the Valmet engine fuelled with natural gas or hydrogen V.RESEARCH AT THE LABORATORY OF TRANSPORT TECHNOLOGY, UGENT It is clear that the Valmet engine with the gas carburetor is of the first generation. These tests have proved that it is not difficult to run an engine on hydrogen (under lean conditions). But it has shown at the same time that special attention is necessary for the power output, the NOx emissions and the backfire problem. The original Valmet diesel engine has a power output of 64 kw, which can be reached also with natural gas (CH ) but not at all with hydrogen (due to the lean The laboratory of Transport Technology at Ghent University is working nearly 15 years on the development and optimization of hydrogen engines. Results of the experimentally work are extensively published. conditions to avoid backfire), see Fig. Sierens (199, 1993). Figure 3 shows the NOx emissions again for natural gas and hydrogen Sierens (199, 1993). At a certain air-fuel ratio the NOx emissions for hydrogen are higher than for natural gas 4 Page 49

5 (and gasoline). Only at very lean mixtures (λ ), the level becomes acceptably low. Rosseel (000). Then a multipoint sequential injection system was installed with a programmable motor management (second generation), Fig. 5. Fig 3: NOx emissions of the Valmet engine The backfire phenomenon is shown in Fig. 4 Sierens and Rosseel (1998). Successive pressure cycles are shown, indicating the runaway pre-ignition till finally the preignition occurs before the inlet valve closure (IVC) (cycle 3) resulting in the explosion of the mixture in the inlet manifold Fig 4: Individual pressure curves of the runaway pre-ignition This (extended) proof of concept on the Valmet engine has indicated the focus of all further research on hydrogen fuelled internal combustion engines: backfire safe operation increase of the power output decrease of the NOx emissions Next a General Motors type 454 engine (better known as the Chevrolet Big Block ) was adapted for gaseous fuels. The engine was initially equipped with a gas carburetor and experiments were carried out with natural gas, mixtures of natural gas and hydrogen, and pure hydrogen Sierens and Fig5: GM engine: view on the multipoint sequential injection system Attention was given to a qualitative control of the load (variation of the richness of the hydrogen-air mixture), beneficial for the engine efficiency compared to a quantitative control using a throttle valve. Also injection duration and ignition maps were optimized, crankcase ventilation and supercharging were applied Sierens (1999), Sierens and Verhelst (000). A single cylinder CFR engine (fixed speed of 600 rpm, variable compression ratio) has been initially equipped with a gas carburetor (first generation), then with a sequential injector (second generation) and is now working with a sequential injector (and MoTeC control unit), exhaust gas recirculation (EGR) and three way catalyst (third generation). Detailed studies are carried out: Pressure measurements in the combustion chamber as a function of load (λ-value), compression ratio, ignition timing etc. Influence of the position of the injector and start of injection on the power output and efficiency. NOx reduction strategies Exhaust gas recirculation (EGR) is an effective means for NOx reduction and an especially interesting option at stoichiometric operation as the high NOx reduction efficiency of a standard three-way catalyst (TWC) can then be exploited. Furthermore, one could vary the engine power output by changing the amount of recycled exhaust gas, instead of throttling, thus avoiding engine efficiency penalties. Page 50

6 [4] Binder K. and Withalm G.: Mixture formation and combustion in hydrogen engine using hydrogen storage technology, International Journal of Hydrogen Energy, 7, , (198). [5] Das L.M.: Hydrogen-oxygen reaction mechanism and its implication to hydrogen engine combustion, International Journal of Hydrogen Energy, 1, , (1996). [6] Das L.M.: Near-term introduction of hydrogen engines for automotive and agricultural application. International Journal of Hydrogen Energy, 7, , (00). [7] Davidson D., Fairlie M., and Stuart A.E.: Development of a hydrogen-fuelled farm tractor, International Journal of Hydrogen Energy, 11, 39 4, (1986). Fig 6: Test rig CFR engine with EGR Two more engines are now fully operated. A onecylinder research engine from the, at that time, Audi-NSU, and further referred to as Audi engine (engine speed rpm).the schematic arrangement of the engine test bench is seen in Fig. 6 The engine is equipped with a high pressure transducer and two injectors (for one cylinder). The ignitionand injection timing are controlled by a MoTeC M4 Pro control unit. Initial results are given by Verstraeten et al. (004). The same measurements and studies as for the CFR engine will be carried out: pressure measurements, backfire studies, exhaust gas recirculation, catalyst studies, supercharging. The latest engine is a Volvo V40 engine, adapted for bi-fuel operation: gasoline or hydrogen (ignition- and injection timing also controlled by a MoTeC control unit. VI.CONCLUSIONS This paper has indicated the advantages of hydrogen as a fuel for spark ignited internal combustion engines and has shown that the hydrogen engine is growing up. An overview is given of the development by car manufacturers and also of the research at the laboratory of Transport Technology, Ghent University. Finally an extended overview is given of the design features in which a dedicated hydrogen engine differs from traditionally fuelled engines. REFERENCES [1] Aceves S.M. and Smith J.R.: Hybrid and conventional hydrogen engine vehicles that meet EZEV emissions. SAE, paper nr 97090, (1997). [] Bardon M.F. and Haycock R.G.: The hydrogen research of R.O. King, Proceedings, 14th World Hydrogen Energy Conference, invited paper, Montreal, Canada, (00). [3] Berckmüller M. et al.: Potentials of a charged SI-hydrogen engine. SAE, paper nr , (003). [8] Furuhama S.: Problems of forecasting the future of advanced engines and engine characteristics of the hydrogen injection with LH tank and pump, Journal of Engineering for Gas Turbines and Power, 119, 7 4, (1997). [9] Gerbig F. et al.: Potentials of the hydrogen combustion engine with innovative hydrogen-specific combustion process, Proceedings, Fisita World Automotive Congress, paper nr F004V113, Barcelona, Spain, (004). [10] Guo L.S., Lu H.B., and Li J.D.: A hydrogen injection system with solenoid valves for a four-cylinder hydrogenfuelled engine, Int. J. of Hydrogen Energy, 4, , (1999). [11] Heffel J.W., McClanahan M.N., and Norbeck J.M.: Electronic fuel injection for hydrogen fueled internal combustion engines. SAE, paper nr 98194, (1998). [1] Heffel J.W., Johnson D.C., and Shelby C.: Hydrogen powered Shelby Cobra: vehicle conversion. SAE, paper nr , (001). [13] Jing-Ding L., Ying-Qing L., and Tian-Shen D.: Improvement on the combustion of a hydrogen fueled engine, International Journal of Hydrogen Energy, 11, , (1986). [14] Kim J.M., Kim Y.T., Lee J.T., and Lee S.Y.: Performance characteristics of hydrogen fueled engine with the direct injection and spark ignition system. SAE, paper nr 95498, (1995). [15] Kondo T., Iio S., and Hiruma M.: A study on the mechanism of backfire in external mixture formation hydrogen engines about backfire occurred by the cause of the spark plug SAE, paper nr , (1997). [16] Koyanagi K., Hiruma M., and Furuhama S.: Study on mechanism of backfire in hydrogen engines. SAE, paper nr 94035, (1994). Page 51

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