ABSTRACT
Hydrogen (H2) internal combustion engines (ICEs) are emerging as an attractive option for applications that require high power, high duty cycle operation due to the relative ease of conversion of existing diesel engines to H2 and the potential for low life-cycle carbon dioxide (CO2) emissions from H2 production and use. For these reasons, H2 ICEs are expected to play a strong role in achieving rapid decarbonization of hard-to-electrify markets such as off-road, rail, and marine.
A unique characteristic of H2 ICEs is their ability to sustain ultra-lean (λ>2) operation. This characteristic also results in relatively low combustion temperature, which helps reduce the likelihood of knock. H2 ICEs have demonstrated acceptable combustion stability across a wide range of λ values. However, results presented in this study indicate that traditional measures of combustion stability such as coefficient of variation of indicated mean effective pressure (COV of IMEP) do not comprehensively represent combustion stability in H2 ICEs. Empirical and simulated data from a heavy duty H2 ICE indicate a high frequency of partial burn cycles can occur even at COV of IMEP values that would otherwise indicate stable combustion. These partial burn cycles result in un-combusted fuel slip, producing inaccurate air-fuel ratio determination and loss of thermal efficiency. Inability to accurately determine air-fuel ratio has implications for critical system functions such as emissions control.
This study seeks to evaluate the validity of COV for reflecting combustion stability in dilute H2 ICEs, and to assess the impact of fuel slip on ICE efficiency and operation. A pre-chamber combustor is proposed as a method for reducing fuel slip and promoting lean stability.
