Combustion Characteristics of the Direct Injection Hydrogen Enriched Compressed Natural Gas Engine at Different Relative Air-Fuel Ratios

Abstract

The implementation of Compressed Natural Gas (CNG) in internal combustion engine (ICE) has many positive benefits such as to improve performance and reduce emission characteristics of the internal combustion engine. However, the engine combustion characteristics are badly affected (i.e. slow burning velocity and poor lean burn capability) as a result of CNG being used in ICE. To this end, research in finding a suitable additives to combine with the CNG becomes necessary. Hydrogen gas (H2) is the best additive to combine with CNG, as it possesses a faster burning and better combustion characteristics. Thus, the primary objective of this research is to conduct experimental investigation on the combustion characteristics of the ICE fuelled with hydrogen enriched compressed natural gas (DI-HCNG) engine at different relative air-fuel ratios λ=1.0, λ=1.2, and λ=1.4 which represent stoichiometric, lean, and very lean combustion respectively. This research was performed experimentally under the following technical operating parameters of the engine: engine speed (at 2000 rpm); percentage of H2 (0%, 28%, and 46% by volume); various air-fuel ratios λ=1.0, λ =1.2, and λ=1.4. The results showed that different percentages of hydrogen gas (H2) directly injected into the CNG engine significantly influenced the maximum in-cylinder pressure, the burning velocity (leading to faster mass fraction burned timings), and the maximum of the heat released rate under all mechanical operating conditions under consideration. Furthermore, the addition of 28% hydrogen gas (H2) to the CNG showed the most stable combustion characteristics relative to 0% and 46%. In light of the above, it can be concluded that direct injection of H2 into the CNG (DI-HCNG) engine would improve the combustion characteristics of the engine (such as faster burning velocity and better lean burn capability).