Strategies for stable operation of a H2 - ICE at high equivalence ratios with use of unburnt and externally injected hydrogen for reducing NOx emissions

Abstract

In this study, the power output of a H2-fuelled internal combustion engine is increased by operating at high equivalence ratios without any issues of backfire or knocking. The coefficient of variation of indicated mean effective pressure is less than 1.2% for the entire range of equivalence ratios, thus indicating the stable operation of the engine. The potential use of hydrogen as a reductant for reducing NOx emissions is exhibited. The engine-out exhaust samples are analyzed for various equivalence ratios, and it is found that a finite amount of unburnt hydrogen is present in the exhaust, which increases with an increase in the equivalence ratio. The unburnt H2 is found to work as a reductant for NOx over a monolithic Pt/Rh catalyst resulting in a low but finite NOx conversion. The NOx conversion is further increased by externally supplying the H2 into the catalytic converter and operating at relatively richer conditions. Under stoichiometric conditions, a NOx conversion of 92% is obtained due to the combination of a high amount of unburnt H2 as well as the reducing conditions over the catalyst which favor the reduction of NOx. At optimized conditions, the torque output is greater than 100 N-m, which is the value recommended by the engine manufacturer for its potential use in a demonstration vehicle. Additionally, despite the operation at high equivalence ratios, the tailpipe NOx concentration is even less than that obtained under ultra-lean conditions. Thus, the engine developed in this work is able to deliver a high torque output while resulting in low NOx emissions.