An experimental study has been conducted to study the effects of hydrogen gas as a dual fuel on the mass fraction burned of the direct injection compressed natural gas engine employing EGR (i.e. DI-CNG-EGR)at various excess a ratios (λ=1.0,1.2,1.3and1.4)which represents to ichiometric, moderately lean, lean and very lean mixtures respectively. The results showed that for a specified EGR rate, the accumulated mass fraction burned shows a quick growing with the increase of hydrogen fractions in the fuel blend; since the flame propagation speed is increased by hydrogen addition. This is evidenced when 46%H2 shows the quickest growth as compared to 28% and 0% respectively with 0% H2 (i.eDI-CNG engine) showing the slowest growth due to the slow burning velocity which natural gas exhibit. The results equally revealed that; increasing the EGR rates, the accumulated mass fraction burned grows up slowly; due to the decreasing in burning (flame propagation) velocity. In furtherance; the part of heat released will be absorbed as a result of introduction of large specific heat capacity gases like CO2and H2O from the exhaust and decreases the combustion temperature and consequent up on this; flame propagation speed decreased. More so, at 0%EGR rate; the total combustion duration at 46%H2 for all the mixtures respectively are 47.0oCA, 40.0oCA, 43.5Oca and 36.5oCA. This shows that very lean mixture (λ=1.4) has the shortest combustion duration whiles to ichio metric mixture (λ=1.0) has the longest combustion duration for the percentage of hydrogen gas under consideration. But when the EGR rate is increased to 17%; the total combustion duration for all the mixtures respectively are: 59.5oCA, 45.5oCA, 36.5oCA, and40.0oCA. This reveals that the shortest combustion duration occur stale an mixture (λ=1.3); while the longest combustion duration still occurs at stoichiometric mixture (λ= 1.0).Thus, it can be concluded that the mass fraction burned of the direct injection compressed natural gas engine are strongly influenced by excess air ratios, hydrogen fractions and EGR; while more stable combustion can be realized at lean mixtures (i.e.λ=1.2, 1.3 and 1.4).
Volume 11 | Issue 1
Pages: 82 - 94