Homogeneous charge compression ignition of hydrogen in a single-cylinder diesel engine

Abstract

Homogeneous charge compression ignition (HCCI) of hydrogen was studied using a single-zone model based in chemical reaction kinetics and using a single-cylinder Cooperative Fuels Research (CFR) diesel engine. Comparison was made with conventional diesel combustion at the same compression ratio and load. Simulation indicated that hydrogen HCCI should be feasible at compression ratios around 18 with intake heating to 100 °C, with peak efficiency occurring for moderately dilute equivalence ratios (0.2–0.5) with the minimum possible amount of intake heating. Experimental hydrogen HCCI was achieved with intake heating to 80 °C and 100 °C for equivalence ratios between 0.15 and 0.37. Hydrogen HCCI exhibited unburned hydrogen emissions of the order of 0.5–1.0 per cent, corresponding to combustion efficiencies of 90–95 per cent. Emissions of nitric oxides were typically below 1 ppm and were at least two orders of magnitude lower than a comparable diesel cycle. Efficiency of hydrogen HCCI was lower than a comparable diesel cycle owing primarily to higher thermal losses and higher chemical enthalpy losses (lower combustion efficiency). These losses are hypothesized to depend strongly on surface area—volume ratio, and methods of mitigating these losses suggest how an engine could be designed to employ hydrogen HCCI.