Effect of equalising ignition delay on combustion and soot emission characteristics of model fuel blends

This paper examines the effect of equalizing ignition delay in a compression ignition engine. Two sets of tests were conducted, i.e. a set of constant injection timing tests with start of fuel injection at 10 degrees crank angle degree (CAD) before top dead center (BTDC) and a set of constant ignition timing tests while also keeping the 10 degrees CAD BTDC injection and adding ignition improver (2-ethylhexylnitrate-, 2-EHN) to the fuel mixtures. Soot particles were characterized using DMS-500 instrument in terms of mass, size, and number. The experimental results showed that adding 2-EHN to the model fuel blends reduced the soot surface area, soot mass concentration and soot mean size. Replacing 20 vol% of a C-7-heptane with 20 vol% methyl-decanoate (an oxygenated C-11 molecule) did not affect the ignition delay or rate of fuel air premixing, the peak in-cylinder pressure or heat release rates. Toluene addition (0-22.5 vol%) to heptane increased the mean size of the soot particles generated by only 3% while also resulted in a slight increase in the peak cylinder pressure and peak heat release rates. Blending toluene and methyl-decanoate into heptane without adding 2-EHN increased the premix phase fraction by at least 13%. However, by adding 2-EHN (4x10(-4)-1.5x10(-3)), the premixed phase fraction decreased by at least 11%.

Automated summary

This paper investigated the effect of equalizing ignition delay in a compression ignition engine, finding that adding an ignition improver reduced soot generation. Different fuel mixtures did not significantly affect ignition delay and fuel air premixing rate.