Numerical simulation of combustion process in a spark-ignition engine fuelled with natural gas-hydrogen blends combined with exhaust gas recirculation

The variations with the crankshaft rotation and 3-dimensional distribution of pressure, temperature, and NO in the cylinder of a natural gas-hydrogen engine were simulated with a hydrogen volume fraction of 20%, excess air ratios (0.9-1.4), and exhaust gas recirculation(EGR) mass fractions (0-0.25) by AVL-FIRE. The predictions of the cylinder pressure agree well with the experimental data, indicating the feasibility of the simulation in the combustion analysis for natural gas-hydrogen engines. The calculation results show that the temperature and pressure in the cylinder, heat released, and the mass fraction of NO decrease, and NO occurs late. The decrease of NO is not obvious when EGR mass fraction is less than 0.15. The use of EGR can be the most effective method to reduce the emission of NO. The yield of NO is the greatest at the excess air ratio of 1.1. Lean mixture combustion is also an important approach to lowering NO emission from natural gas-hydrogen engines.