A comprehensive Modeling Study of Natural Gas (HCCI) Engine Combustion Enhancement by Using Hydrogen Addition

A zero-dimensional, thermodynamic model with detailed chemical kinetics and cylinder wall heat transfer correlations has been used to study the detailed oxidation mechanism of natural gas in homogeneous charge compression ignition (HCCI) engine. A short mechanism made up of 241 reversible elementary reactions among 47species has been assembled from a previously extended detailed mechanism. The mechanism was numerically investigated at different operating and geometry conditions of HCCI engine during the time period in which both intake and exhaust valves are closed. The study is performed to elucidate the mechanisms of extinction and combustion behaviors of natural gas fuel with the effect of hydrogen addition to overcome the control of autoignition timing over a wide range of speeds and loads, limiting the heat released rate at high load operation, and meeting emission standards. The results indicate that if the initial conditions of natural gas mixture have been known precisely at intake valve closing, then the autoignition timing and combustion efficiency are controllable. For the same intake condition, the mixture containing a small quantity of hydrogen was ignited rather than that without hydrogen. The cycle simulations using hydrogen as an additive to the natural gas, have elucidate the critical factors controlling the engine's combustion performance and emissions, and suggest the limits of possible improvement relative to conventional NG (HCCI) engine technologies.