Effects of natural-gas blending on ignition delay and pollutant emission of diesel fuel for the condition of homogenous charge compression ignition engine

Burning of dual fuel of diesel and natural gas is a promising technique in compression ignition engine in the aspects of fuel economy and reduced emission. Effects of blending of natural gas with diesel fuel are investigated numerically and experimentally with respect to ignition delay, heat production, and pollutant emission. First, major properties of diesel are measured at high pressure of 40 bar, which is an engine-relevant condition, and thereby, a surrogate fuel with higher accuracy is formulated, which has properties closer to diesel than the other existing surrogate fuels. Especially, as one of key properties, high molecular weight of diesel is considered critically in formulating a surrogate fuel. Ignition delay times of several mixtures of diesel and natural gas (NG), of which mixture ratios of 100/0%, 60/40%, and 20/80%, are measured by a shock tube in the ranges of temperature from 770 K to 1,000 K and of equivalence ratios from 0.5 to 2.0. Measured ignition delay is compared with that calculated by numerical simulations with the surrogate fuel formulated in this study for its validation. Finally, combustion simulations of HCCI (homogeneous charge compression ignition) are conducted with the mixture of diesel and NG and compared with available experimental data. And thereby, optimal mixture ratio of the dual fuel is suggested in terms of ignition time and pollutant emission acceptable in HCCI engines.

Automated summary

The burning of a mixture of diesel and natural gas shows potential in achieving better fuel economy and reduced emission. This study investigates the effects of blending natural gas with diesel fuel on ignition delay, heat production, and pollutant emission through numerical and experimental methods. A surrogate fuel with high accuracy is formulated to closely simulate the properties of diesel. The study also suggests an optimal mixture ratio for the dual fuel based on ignition time and acceptable pollutant emission in HCCI engines.