An experiment on a 20% hydrogen enriched CNG(HCNG)engine was conducted.Based on the fitting relationship between air-gas mixture flow rate,inlet manifold absolute pressure,engine speed and throttle opening degree,empirical formulas were proposed to predict air-gas mixture flow rate and inlet manifold absolute pressure,and an approximate linear relationship between the product of inlet manifold absolute pressure and effective thermal efficiency(p_(man)η_e)and the product of inlet manifold absolute pressure a...