HCNG for sustainable emission reduction in SI engines

Abstract

As the urgency for environmental protection and the need for alternative energy sources grow, the quest for substitutes for petroleum has become increasingly critical. Natural gas, mainly comprised of methane, is one of the finest alternative fuels with advantageous properties like a high hydrogen-to-carbon (H/C) ratio and octane number. Nevertheless, natural gas engines that operate on spark ignition (SI) encounter challenges, including slow combustion rates and restricted lean-burn capabilities, which lead to considerable variations from cycle to cycle, diminished power output, and higher fuel consumption. Consequently, it is vital to improve the combustion process under lean conditions. A viable approach to this issue is incorporating hydrogen, which is thought to mitigate these challenges. Blending of hydrogen increases the combustion rate and stability of natural gas, resulting in improved efficiency, shorter burn times, and a broader range of lean operation. This research examines the effects of adding various levels of hydrogen to compressed natural gas (CNG) in a 3-cylinder internal combustion engine (ICE). The performance, emissions, and combustion characteristics were analyzed at various equivalence ratios, utilizing brake torques, spark timing, and throttle conditions. The results demonstrated that increased hydrogen content improves brake thermal efficiency in lean conditions, achieving a peak brake thermal efficiency of 23 % at 2500 rpm with a blending of 5 % hydrogen, but declining with higher hydrogen concentrations. Significant enhancements in brake thermal efficiency were observed. Blending of hydrogen with CNG resulted in a reduction in releases of carbon monoxide (CO), hydrocarbons (HC), and carbon dioxide (CO2) compared to standard CNG. However, it was noted that nitrogen oxides (NOx) emissions increased for hydrogen-enriched compressed natural gas (HCNG) as compared to CNG.