Experimental investigation on the effect of natural gas premixed ratio on combustion and emissions in an IDI engine

Abstract

Usage of natural gas in an internal combustion engine that has different combustion technologies is considered a possible solution to reduce engine outlet emissions and lower fuel consumption. A single-cylinder IDI engine, a variable compression ratio engine equipped with a mechanical pumping diesel fuel that can change the timing of starting a fuel injection from 0° to 45° before TDC, for the empirical study of combustion and pollutants is tested. Computational fluid dynamics simulation with detailed chemical kinetic mechanisms is compared with experimental results. Experimental results are evaluated in two different engines loads of 25%, 60%, and 1100 rpm. Four cases are tested with different natural gas ratio and the same start of diesel fuel injection. Increasing the formation and release of HC and CO pollutant occurs with an increase in premix natural gas due to incomplete combustion. Furthermore, by increasing the percentage of natural gas from case 1 to 4, the reduction of NOx in the engine output occurs by increasing the natural gas ratio and at the end, reducing HC and CO emissions happen by increasing engine loading and combustion improvement. Also, in-cylinder pressure at the compression stage decreases with an increase in natural gas ratio because with the increase in the mixing of natural gas fuel with air, the special heat capacity of the mixture increases.