Hydrogen for IC Engines: A Review Vinayaka S, Syed farees khaleel rahman H.K, Nawaz Shariff & P Vamsi dhar Reddy Department of Mechanical Engineering, Atria Institute of Technology, Bangalore E-mail : vink.v8@gmail.com, sfr.farees@gmail.com, nawazoaj@gmail.com, suppervamsi@gmail.com Abstract Hydrogen provides a pathway for energy diversity. It can store the energy from diverse domestic resources (including clean coal, nuclear, and intermittently available renewables) for use in mobile applications and more. Vehicles operating on hydrogen can dramatically reduce our nation s dependence on oil and significantly reduce tailpipe emissions. Hydrogen offers a potential means to store and deliver energy from abundant, domestically available resources while reducing our nation s carbon footprint. This paper describes the use of Hydrogen as a fuel in IC engines and the technical aspects that accompany this idea. I. INTRODUCTION The very first hydrogen powered automobile technology which was developed in year 1806. Though hydrogen as a fuel is popularly known in propelling rockets, the very idea to power an on road automobile is not new. It is believed that lack of technology back proved to be a bane to carry forward the idea. The advancements in present day engine technology have enabled us to use alternate fuels like hydrogen to power our locomotives. II. REASONS FOR CHOOSING HYDROGEN Hydrogen is the most abundant element present on earth. [8] The ever increasing demands for fossil fuels have left us with very miniscule reservoirs. Increase in global warming due to the emission of carbonaceous matter to the atmosphere. Need to develop efficient engines in order to improve transportation. Hydrogen has a very high calorific value compared hydrocarbons. It is not a pollutant and also does not contaminate the ground water. [8] III. PROPERTIES OF HYDROGEN A. Wide Range of Flammability Hydrogen has a wide flammability range in comparison with all other fuels. As a result, hydrogen can be combusted in an internal combustion engine over a wide range of fuel-air mixtures. A significant advantage of this is that hydrogen can run on a lean mixture. Generally, fuel economy is greater and the combustion reaction is more complete when a vehicle is run on a lean mixture. B. Low Ignition Energy Hydrogen has very low ignition energy. The amount of energy needed to ignite hydrogen is about one order of magnitude less than that required for gasoline. This enables hydrogen engines to ignite lean mixtures and ensures prompt ignition. C. Small Quenching Distance Hydrogen has a small quenching distance, smaller than gasoline. Consequently, hydrogen flames travel closer to the cylinder wall than other fuels before they extinguish. Thus, it is more difficult to quench a hydrogen flame than a gasoline flame. D. High Auto-Ignition Temperature Hydrogen has a relatively high auto ignition temperature. This has important implications when a hydrogen-air mixture is compressed. In fact, the auto ignition temperature is an important factor in determining what compression ratio an engine can use, since the temperature rise during compress ion is related to the compression ratio. E. High Flame Speed Hydrogen has a high flame speed at stoichiometric ratios. Under these conditions, the hydrogen flame speed is nearly an order of magnitude higher than that of gasoline. This means that hydrogen engines can more closely approach the thermodynamically ideal engine cycle. 68
F. High Diffusivity Hydrogen has very high diffusivity. This ability to disperse in air is considerably greater than gasoline and is advantageous for two main reasons. Firstly, it facilitates the formation of a uniform mixture of fuel and air. Secondly, if a hydrogen leak develops, the hydrogen disperses rapidly. Thus, unsafe conditions can either be avoided or minimized. IV. DESIGN OF HYDROGEN ENGINES A disk-shaped combustion chamber (with a flat piston and chamber ceiling) can be used to reduce turbulence within the chamber. The disk shape helps produce low radial and tangential velocity components and does not amplify inlet swirl during compression. Since unburned hydrocarbons are not a concern in hydrogen engines, a large bore-to-stroke ratio can be used with this engine. To accommodate the wider range of flame speeds that occur over a greater range of equivalence ratios, two spark plugs are needed. The cooling system must be de- signed to provide uniform flow to all locations that need cooling. Additional measures to decrease the probability of pre-ignition are the use of two small exhaust valves as opposed to a single large one, and the development of an effective scavenging system, that is, a means of displacing exhaust gas from the combustion chamber with fresh air. V. ACCESSORIES THAT COMPLETE THE DESIGN A. Crankcase Ventilation [5] Crankcase ventilation is even more important for hydrogen engines than for gasoline engines. As with gasoline engines, unburnt fuel can seep by the piston rings and enter the crankcase. Since hydrogen has a lower energy ignition limit than gasoline, any unburnt hydrogen entering the crankcase has a greater chance of igniting. Hydrogen should be prevented from accumulating through ventilation. Ignition within the crankcase can be just a startling noise or result in engine fire. When hydrogen ignites within the crankcase, a sudden pressure rise occurs. To relieve this pressure, a pressure relief valve must be installed on the valve cover. B. Storage Hydrogen has a very low volumetric energy density at ambient conditions. Even when the fuel is stored as a liquid in a cryogenic tank or in a compressed hydrogen storage tank, the volumetric energy is small relative to that of gasoline. Hydrogen has a three times higher calorific value compared to gasoline (143 MJ/kg versus 46.9 MJ/kg). Some research has been done into using special crystalline materials to store hydrogen at greater densities and at lower pressures. [3] C. Type of Fuel Delivery System [4] i) Port Injection System The port injection fuel delivery system injects fuel directly into the intake manifold at each intake port, rather than drawing fuel in at a central point. Typically, the hydrogen is injected into the manifold after the beginning of the intake stroke. At this point conditions are much less severe and the probability for premature ignition is reduced. The two types of port injection system are constant volume injector and electronic fuel injector. ii) Direct Injection System In direct injection, the intake valve is closed when the fuel is injected, completely avoiding premature ignition during the intake stroke. Consequently the engine cannot backfire into the intake manifold. The power output of a direct injected hydrogen engine is 20% more than for a gasoline engine and 42% more than a hydrogen engine using a carburettor. iii). Central Injection System The simplest method of delivering fuel to a hydrogen engine is by way of a carburettor or central injection system. This system has advantages for a hydrogen engine. Firstly, central injection does not require the hydrogen supply pressure to be as high as for other methods. Secondly, central injection or carburettors are used on gasoline engines, making it easy to convert a standard gasoline engine to hydrogen or a gasoline/hydrogen engine. D. Ignition System [5] Due to hydrogen s low ignition energy limit, igniting hydrogen is easy and gasoline ignition systems can be used. At very lean air/fuel ratios (130:1 to 180:1) the flame velocity is reduced considerably and the use of a dual spark plug system is preferred. Ignition systems that use a waste spark system should not be used for hydrogen engines. These systems energize the spark each time the piston is at top dead centre whether or not the piston is on the compression stroke or on its exhaust stroke. For gasoline engines, waste spark systems work well and are less expensive than other systems. For hydrogen engines, the waste sparks are a source of pre-ignition. 69
Spark plugs for a hydrogen engine should have a cold rating and have non-platinum tips. A cold-rated plug is one that transfers heat from the plug tip to the cylinder head quicker than a hot-rated spark plug. This means the chances of the spark plug tip igniting the air/fuel charge is reduced. Hot- rated spark plugs are designed to maintain a certain amount of heat so that carbon deposits do not accumulate. Since hydrogen does not contain carbon, hot-rated spark plugs do not serve a useful function. VI. EFFICIENCY The high octane and low lean-flammability limit of hydrogen provides the necessary elements to attain high thermal efficiencies in an engine. Brake thermal efficiency (BTE) versus brake mean effective pressure (BMEP) for various sources is plotted in Fig. 1. Direct comparison between the various studies have found compression ratio of approximately 14.5:1 to be optimal due to heat transfer losses at higher CR. [4, 6] Besides the increase in BTE, by increasing compression ratio, engines have higher efficiencies than gasoline engines at similar CR. This is observed by comparing the gasoline and hydrogen data sets of experimental hydrogen fuelled automotive engine design data base project [5]. Compared to gasoline operation the BTE with hydrogen operation is higher across the entire operating range, with the relative increase maximum at medium loads. The drop-off in the relative difference in BTE between gasoline and hydrogen at low loads is due to the need for some throttling. heat transfer to the cylinder walls increases monotonically with increasing equivalence ratio. The trend is explained as a consequence of increasing flame velocity, increasing flame temperature and decreasing quenching distance with increasing equivalence ratio that leads to narrow thermal boundary layers. VII. POWER DEVELOPED The theoretical maximum power output from a hydrogen engine depends on the air/fuel ratio and fuel injection method used. The stoichiometric air/fuel ratio for hydrogen is 34:1. At this air/fuel ratio, hydrogen will displace 29% of the combustion chamber leaving only 71% for the air. As a result, the energy content of this mixture will be less than it would be if the fuel were gasoline (since gasoline is a liquid, it only occupies a very small volume of the combustion chamber, and thus allows more air to enter). Since both the carburetted and port injection methods mix the fuel and air prior to it entering the combustion chamber, these systems limit the maximum theoretical power obtain able to approximately 85% of that of gasoline engines. For direct injection systems, which mix the fuel with the air after the intake valve has closed (and thus the combustion chamber has 100% air), the maximum output of the engine can be approximately 15% higher than that for gasoline engines. [3] Therefore, depending on how the fuel is metered, the maxi- mum output for a hydrogen engine can be either 15% higher or 15% less than that of gasoline if a stoichiometric air/fuel ratio is used. However, at a stoichiometric air/fuel ratio, the combustion temperature is very high and as a result it will form a large amount of nitrogen oxides (NOx), which is a criteria pollutant. Since one of the reasons for using hydrogen is low exhaust emissions, hydrogen engines are not normally designed to run at a stoichiometric air/fuel ratio. [4] VIII. EMISSIONS The combustion of hydrogen with oxygen produces water as its only product: 2H 2 + O 2 = 2H 2 O The combustion of hydrogen with air however can also produce oxides of nitrogen (NOx): The drop-off at high loads is likely due to increasing heat transfer losses [7] shows that for an engine the relative fraction of the heat release lost by H 2 + O 2 + N 2 = H 2 O + N 2 + NO x The oxides of nitrogen are created due to the high temperatures generated within the combustion chamber during combustion. This high temperature causes some of the nitrogen in the air to combine with the oxygen in the air. The amount of NOx formed depends on: 70
The air/fuel ratio The engine compression ratio The engine speed The ignition timing Thermal dilution IX. MAJOR DRAWBACK One of the most critical obstacles in developing hydrogen technology is its storage and transport. The problem is easily seen by comparing the energy to volume ratio for gaseous hydrogen (3.0MJ/L) to that of conventional gasoline (32.0MJ/L). This means that, given the same volume, the energy produced by hydrogen is about ten times lower than that from conventional gasoline. This obviously represents a problem for storing hydrogen in a vehicle, for example: a big, heavy tank would be required to store and transport the required amount of hydrogen. Some possible solutions are to use liquid hydrogen (8.5MJ/L), to use compressed hydrogen or to store hydrogen in solid metallic support such as metal complexes (hydrides). The use of compressed hydrogen implies using liquid tanks that need to be made of a very strong, lightweight material. This material should also have outstanding insulating and pressurization properties, in order to avoid hydrogen leakage. This problem can potentially be solved using nanotechnology to develop new materials with exceptional properties in terms of strength and density. X. DISTIBUTION INFRASTRUCTURE [9] Regardless of range, every vehicle needs fuel at some point. And here lies hydrogen s chicken and-egg problem: fuel-cell vehicles will never sell in a big way until there is a viable network of service stations to fuel them. But no one is going to invest the capital required to create such a network until there is a fleet of thirsty hydrogen vehicles to provide a market. Hydrogen pumps can and have been added to existing petrol stations, where at first glance they look much the same as conventional pumps. Because the hydrogen used is a compressed gas, filling the tank is not just a matter of placing a nozzle in the petrol-tank opening and letting gravity take care of the rest. Instead, a tight seal has to be established between the nozzle and car, and high-powered pumps have to force hydrogen through the nozzle until the desired pressure is reached. In practice, the current-generation hydrogen pumps are already easy and safe enough for an average consumer to use. But they do have to work perfectly if tanks are to be filled to full pressure; at present their performance is solid but variable. XI. APPLICATIONS [10] In 2003 Mazda developed a bi-fuel sports car called Mazda RX-8 RE Hydrogen. This car had the same twin rotor Wankel engine which used both hydrogen and Petrol, and was first developed in 1991(used in Mazda HR-X). This car had a hydrogen tank of 110 liters stored at 350 bar, and was also equipped with a petrol tank of 61 liters. The engine had an equivalent displacement of 2616cc. It produced 154 KW and 222 Nm if torque at 5000 RPM while running on petrol. It produced 80KW and 140 Nm of torque at 5000 RPM while using Hydrogen as fuel. The range of this car was 100 Km using full tank of hydrogen, and 550Km using full tank of petrol. Fig.2 Mazda RX-8 RE Hydrogen In 2007 BMW developed 2 cars Hydrogen 7 and H2R which used the same duel fuel 6000cc V12 engine. The output of this engine was 191 KW and 390 Nm of torque. The hydrogen 7 was equipped with a hydrogen fuel tank which stored 8kg of hydrogen and also had a petrol tank which stored 36 litres. The range of Hydrogen 7 was 200 Km on hydrogen and 480 Km of petrol. BMW H2R holds the record as the fastest hydrogen fuelled car, as it has reached 301 Km/h. Fig.3 BMW H2R 71
Fig 4 BMW Hydrogen 7 XII. CONCLUSION As research progresses, the technologies used to produce the hydrogen are expected to shift toward those that produce no net greenhouse gas emissions. While some of the hydrogen production technologies now under development may be supplanted by competing or improved approaches, a variety of production technologies are likely to find long-term use in regions that offer an abundance of their required feedstock and renewable energy resource. Fuel costs to consumers will gradually decrease as these technologies and the delivery infrastructure are optimized and grow to maturity. Ultimately, hydrogen represents an important component of our national strategy to diversify energy resources. The use of hydrogen in IC engines can be realised by reducing the weight of the automobile and development of better auxiliary systems. The current technology uses petrol methane etc. in order to increase the range of the vehicle. Hence the goal of researchers is to develop automobiles which use only hydrogen as the only fuel. XIII. REFERENCES [1] Veziroglu TN.1987, International Journal of Hydrogen Energy 12:99 INSPEC Compendex [2] Winter CJ.1987, International Journal of Hydrogen Energy 12:521 INSPEC Compendex [3] Swain MR, Pappas JM, Adt Jr RR, Escher WJD. Hydrogen- fuelled automotive engine experimental testing to provide an Initial design-data base. SAE paper 1981; 810350. [4] Tang X, Kabat DM, Natkin RJ, Stockhausen WF. Ford P2000 hydrogen engine dynamometer development. SAE paper 2002; 2002-01-0242. [5] Swain MR, Adt Jr RR, Pappas JM. Experimental hydrogen- fueled automotive engine design data base project. Technical report, A Facsimile Report, Prepared for U.S. Department of Energy, DOE/CS/51212, 1983. [6] Nagalingam B, Dübel M, Schmillen K. Performance of the supercharged spark ignition hydrogen engine. SAE paper 1983; 831688 [7] Shudo T, Nabetani S, Nakajima Y. Analysis of the degree of constant volume and cooling loss in a spark ignition engine fuelled with hydrogen. Int J Engine Research 2001;2:81-92. [8] Hydrogen Production Overview of Technology Options [9] Fuel of the Future?, NATURE Vol 464 Vol 464 29 April 2010 [10] www.howstuffworks.com 72