Combustion Characteristics of Hydrogen-Natural Gas Mixtures in Passenger Car Engines

Abstract

<div class="htmlview paragraph">The presented concept in this study consists of a state of the art passenger car natural-gas engine fired by different hydrogen (H<sub>2</sub>) and compressed-natural-gas (CNG) fuel blends. The hydrogen content in the fuel was varied among 5 and 15vol% corresponding to 0.6-2.1 mass%, while comparisons include also engine operation on pure CNG.</div> <div class="htmlview paragraph">Increasing hydrogen content of the fuel accelerated combustion leading to modest efficiency improvements. Combustion analysis showed that the increasing burning rates mainly affected the initial combustion phase (duration for 5% mass fraction burned).</div> <div class="htmlview paragraph">With optimal combinations of spark timing and EGR rate the achievements are additional efficiency increase with substantially lower engine-out NO<sub>x</sub> while total unburned hydrocarbons or CO-engine-out emissions are not affected.</div> <div class="htmlview paragraph">Investigations using Design of Experiments (DoE) algorithms provided a comprehensive picture of the entire parameter space. The investigations showed two fuel consumption optimal combustion domains: Low EGR and late spark timing with associated high engine-out NO<sub>x</sub> emissions as well as high EGR and early spark timing with very low engine-out NO<sub>x</sub>.</div>