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Cycle-by-cycle Variations in a Direct Injection Hydrogen Enriched Compressed Natural Gas Engine Employing EGR at Relative Air-Fuel Ratios.

机译:在相对空燃比下使用EGR的直喷富氢压缩天然气发动机的逐周期变化。

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Since the pressure development in a combustion chamber is uniquely related to the combustion process, substantial variations in the combustion process on a cycle-by-cycle basis are occurring. To this end, an experimental study of cycle-by-cycle variation in a direct injection spark ignition engine fueled with natural gas-hydrogen blends combined with exhaust gas recirculation at relative air-fuel ratios was conducted. The impacts of relative air-fuel ratios (i.e. λ = 1.0, 1.2, 1.3 and 1.4 which represent stoichiometric, moderately lean, lean and very lean mixtures respectively), hydrogen fractions and EGR rates were studied. The results showed that increasing the relative air-fuel ratio increases the COVIMEP. The behavior is more pronounced at the larger relative air-fuel ratios. More so, for a specified EGR rate; increasing the hydrogen fractions decreases the maximum COVIMEP value just as increasing in EGR rates increases the maximum COVIMEP value. (i.e. When percentage EGR rates is increased from 0% to 17% and 20% respectively. The maximum COVIMEP value increases from 6.25% to 6.56% and 8.30% respectively). Since the introduction of hydrogen gas reduces the cycle-by-cycle combustion variation in engine cylinder; thus it can be concluded that addition of hydrogen into direct injection compressed natural gas engine employing EGR at various relative air-fuel ratios is a viable approach to obtain an improved combustion quality which correspond to lower coefficient of variation in imep, (COVIMEP ) in a direct injection compressed natural gas engine employing EGR at relative air-fuel ratios.Key words: Coefficient of variation in indicated mean effective pressure (COVIMEP) / Direct injection compressed natural gas (DI-CNG) / Exhaust gas recirculation (EGR) / Hydrogen fractions / Relative air-fuel ratios.
机译:由于燃烧室内的压力发展与燃烧过程是唯一相关的,因此在燃烧过程中会出现逐周期变化。为此,进行了以天然气-氢混合气为燃料的直喷式火花点火发动机在相对空燃比下结合废气再循环的逐周期变化的实验研究。研究了相对空燃比(即分别代表化学计量比,中度稀薄,稀薄和非常稀薄的混合物的λ= 1.0、1.2、1.3和1.4),氢气分数和EGR率的影响。结果表明,增加相对空燃比会增加COVIMEP。在较大的相对空燃比下,该行为更为明显。对于指定的EGR率,更是如此;增加氢气分数会降低最大COVIMEP值,就像增加EGR率会增加最大COVIMEP值一样。 (即,当EGR率百分比分别从0%增加到17%和20%时。最大COVIMEP值分别从6.25%增加到6.56%和8.30%)。由于引入氢气减少了发动机气缸内逐周期燃烧变化;因此可以得出结论,以不同的相对空燃比向采用EGR的直喷压缩天然气发动机中添加氢气是一种获得改善的燃烧质量的可行方法,该燃烧质量对应于较低的imep变化系数(COVIMEP)。相对空燃比采用EGR的直喷压缩天然气发动机关键词:指示平均有效压力(COVIMEP)/直喷压缩天然气(DI-CNG)/排气再循环(EGR)/氢气分数的变化系数/相对空燃比。

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