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In the future, our energy systems will need to be renewable and sustainable, efficient and costiveness, convenient and safe. Hydrogen is expected to be one of the most important fuels in the near future to meet the stringent emission norms. The use of the hydrogen as fuel in the internal combustion engine represents an alternative use to replace the hydrocarbons fuels, which produce polluting gases such as carbon monoxide (CO), hydro carbon (HCI) during combustion. In this paper contemporary research on the hydrogen- fueled internal combustion engine can be given.
However, increase in stringent environment regulations on exhaust emissions and anticipation of the future depletion of worldwide petroleum reserves revised strong encouragement for research on alternative fuels As a result various alternative fuels (such as liquefied petroleum gas (ALP), compressed natural gas (CNN), hydrogen, vegetable oils, bio gas, producer gas) have been considered as substitutes for hydrocarbon-based fuel and reducing exhaust emissions. Of these, hydrogen is a long-term renewable and less-polluting fuel. In addition hydrogen is clean burning characteristics and better performance drives more interest in hydrogen fuel.
When it is burnt in an internal combustion engine, the primary combustion product is water with no CO. Although Knox missions are formed when hydrogen is used [2,71 1. 1 . Combustive Properties of Hydrogen There several important characteristics of hydrogen that greatly influence the technological development of hydrogen internal combustion engine. 1. 1. 1. Wide range of flammability Compared to nearly all other fuels, hydrogen has a wide flammability range (475% versus 1. 4-7. 6% volume in air for gasoline). This first leads to obvious concerns over the safe handling of hydrogen.
But, it also implies that a wide range of failure mixtures, including a lean mix of fuel to air, or, in other words, a fuel-air mix in which the amount of fuel is less than the psychometric, or chemically ideal, amount. Running an engine on a lean mix generally allows for greater fuel economy due to a more complete combustion Of the fuel. In addition, it also allows for a lower combustion temperature, lowering emissions of criteria pollutants such as nitrous oxides (Knox) [3]. 2 1. 1 . 2. Small quenching distance Hydrogen has a small quenching distance (0. 6 mm for hydrogen versus 2. Mm for gasoline), which refers to the distance from the internal cylinder wall where the combustion flame extinguishes. This implies that it is more difficult to ounce a hydrogen flame than the flame of most other fuels, which can increase backfire since the flame from a hydrogen-air mixture more readily passes a nearly closed intake valve, than a hydrocarbon-air flame [3, 17]. 1. 1. 3. Flame velocity and adiabatic flame Hydrogen burns with a high flame speed, allowing for hydrogen engines to more closely approach the thermodynamically ideal engine cycle (most efficient fuel power ratio) when the psychometric fuel mix is used.
However, when the engine is running lean to improve fuel economy, flame speed slows significantly [3]. Flame velocity and adiabatic flame enrapture are important properties for engine operation and control, in particular thermal efficiency, combustion stability and emissions. Laminar flame velocity and flame temperature, plotted as a function of equivalence ratio, are shown in Fig. 1. And Fig 2. , respectively. Fig. 1 . Adiabatic flame temperature for hydrogen-air mixtures [5]. 3 ignition of the charge in the combustion chamber. 1. 1. 5.
High diffusivity Fig. 2. Laminar flame velocity for (??) hydrogen, oxygen and nitrogen mixtures and (e, – -) gasoline and air mixtures 1. 1. 4. Minimum ignition source energy The minimum ignition source energy s the minimum energy required to ignite a fuel-air mix by an ignition source such as a spark discharge. For a hydrogen and air mix it is about an order of magna etude lower than that of a petrol-air mix 0. 02 m] as compared to 0. 24 ms for petrol – and is approximately constant over the range of flammability. This is illustrated in Fig 3.
Unfortunately, the low ignition energy means that hot gases and hot spots on the cylinder can serve as sources of ignition, creating problems of premature ignition and flashback Fig. 3. Minimum ignition energy of hydrogen in air [4] The low minimum ignition energy of he hydrogen-air mix means that a much lower energy spark is required for spark ignition. This means that combustion can be initiated with a simple glow plug or resistance hot-wire. It also ensures prompt Hydrogen has very high diffusivity. This ability to disperse into air is considerably greater than gasoline and is advantageous for two main reasons.
Firstly, it facilitates the formation off 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 [6]. 1. 1. 6. Low density The most important implication of hydrogen’s low density is that without significant compression or conversion of hydrogen to a liquid, a very large volume may be necessary to store enough hydrogen to provide an adequate driving range. Low density also implies that the fuel-air mixture has low energy density, which tends to reduce the power output of the engine.
Thus when a hydrogen engine is run lean, issues with inadequate power may arise 1. 1. 7. High auto-ignition temperature The auto ignition temperature is the minimum temperature required to initiate self-sustained combustion in a combustible fuel mixture in the absence of an external ignition. For hydrogen, the auto ignition temperature is relatively high CHIC. This makes it difficult of ignite a hydrogen??air mixture on the basis of heat alone without some additional ignition source. The auto ignition temperatures of various fuels are shown in Table 1. This temperature has important implications when a hydrogen-air mixture is compressed.