Mass Fraction Burned of the Direct-injection Hydrogen Enriched Compressed Natural Gas Engine Employing Exhaust Gas Recirculation

Saheed Wasiu, A.A. Rashid and W.M. Wan Muhamad

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