Experimental Study On Combustion And Emission Characteristics And Quasi-Dimensional Modeling Computation Of A HCNG Engine

Hydrogen enriched natural gas is short for HCNG. It is not only an alternative fuel meeting the demand of automobile developing"saving energy and reducing emission", but also acts as a feasible way to transform vehicle fuel from conventional fuel to hydrogen energy. HCNG engine is the focus of this thesis and there are two main parts, one is modeling computation on HCNG engine, and the other is experimental study on combustion and emission characteristics.In the modeling part, first the equations are carried out for computing H2/NG ratio in mass, stoichiometric ratio and heat value of fuel-air mixture on various H2 fractions in volume. Second the methods are introduced to calculate the theoretical adiabatic flame temperature and laminar burning velocity of HCNG mixture. Then based on the physical and chemical properties and combustion characteristics of HCNG, the two-zone quasi-dimensional combustion model of HCNG fueled engine is set up to predict the engine performance under twelve operation conditions. Finally the predicted results are compared with that of engine actually operating, in order to testify the applicability of this model. The meaning of setting this model up is that it can not only simulate all the operation conditions to save the lab cost, but also optimize the parameter of engine such as compress ratio, the shape of combustion chamber, which are not easy to modify.In the experimental part, the object of the study is combustion and emission characteristics of HCNG fueled engine, including two series of experiment, one is that spark ignition timing is changed and all the other parameter are fixed, the other is that excess air ratio is changed. The results shows that the maximum brake torque timing(MBT) gets closer to the TDC and the indicated thermal efficiency increases with the increase of hydrogen blend ratio. The addition of hydrogen can extend the lean operation limit, and leaner burn can reduce NOx emission obviously, which is the important meaning of hydrogen addition. Before lean operation limit, the indicated thermal efficiency increases with the excess air ratio rises. The NOx, CO and HC emissions all descend with the increase of spark advance angle, and ascend with the increase of the MAP, so in the actual engine operation, the spark advance angle should be as closer to TDC as it can maintain the engine torque. Under the same ignition timing and excess air ratio, with increasing the hydrogen blend ratio the NOx and CO emissions increase, and HC emission decreases.Finally to summarize the results above, as the direction of calibrating HCNG fueled engine, it can be concluded that the air fuel ratio should be leaner than that of CNG engine, and ensuring to maintain the engine torque, the minimum spark advance angle should be selected as the ignition timing.