An Investigation On The Combustion And NO_x Emission Simulation Of A Biogas Diesel Duel-Fuel Engine

Biogas is a kind of alternative clean fuel for engine. It is one of the most important way to solve the shortage of energy. In our country the biogas is used more and more widely in engine. Biogas—diesel dual fuel engine is refitted from the ZH1115 direct injection diesel engine. Biogas is induced through intake tube with air during intake stroke. The diesel is injected in the cylinder at the end of the compression stroke and ignites the biogas.In this paper, NO_x formation model of biogas — diesel dual fuel engine was established, which combines the quasi-dimensional spray combustion model based on Hiroyuki Hiroyasu's model with the detailed chemical kinetics mechanism of NO_x formation. The model has good precision compared with experiment data.Based on the NO_x formation model, the influence of engine speed, load and fuel supply advance angle to the NO_x emission is then carried out. The NO_x emission of dual fuel engine is 30% — 80% lower than diesel engine. When the load of the biogas—diesel dual fuel engine increases and the engine speed is at the same, its ignition time is advanced, its ignition delay period is shorter, its maximum heat release rate and temperature are larger, NO_x emission will increase. At low speed and high load the biogas—diesel dual fuel engine has a higher volumetric efficiency, the time of the mixture staying at high temperature level is longer, so even if the maximum combustion temperature is relatively lower, the NO_x emission is still high. The delay of the fuel supply advance angle leads to lower pre-mixed combustion rate and maximum pressure, NO_x emission will decrease.