Experimental Investigation Of A Hydrogen-blended Gasoline Rotary Engine

Rotary engines have characteristics of compact construction, small weight, high power-to-weight ratio and good operating stability. However, the combustion of rotary engines is generally narrow, and the rotary engine always runs at high speeds. These could easily cause the difficulties in flame propagation for the liquid fuels combustion, which finally leads to the increased fuel consumption and toxic emissions. Improving the flame propagation speed and reducing the brake specific fuel consumption and toxic emissions are key for the practical application of rotary engines. The hydrogen has characteristics of low ignition engine, high diffusive and propagation speed, high flame temperature and wide flammability limit which are beneficial for ensuring the stable ignition and fast flame propagation for the rotary engines. Thus, the rotary engine could gain higher thermal efficiency and lower toxic emissions through the hydrogen combustion. However, the combustion of pure hydrogen in the rotary engines has problems of increased hydrogen consumption rate and difficulties in lubrication. Comparatively, blending small amounts of hydrogen through port injection could also improve the combustion of rotary engines. This also alleviates concerns on the cost and hydrogen consumption rates. Thus, the research and development in the hydrogen-blended rotary engines is more important for the practical application of rotary engines. This investigation experimentally studied the combustion and emissions characteristics of a hydrogen-blended rotary engine.To conduct experiments for the hydrogen-blended rotary engine, a hydrogen-blended gasoline rotary engine testing bench was designed and built. A spark module and a hydrogen-gasoline injection system were newly developed for testing rotary engine. A self-developed hybrid electronic control unit?HECU? was employed to control the ignition, injection durations of gasoline and hydrogen. The global excess air ratio and hydrogen volume fraction in the intake of the mixtures were adjusted by changing the gasoline and hydrogen injection durations. A combustion and heat release analysis computing program was proposed by this investigation. The rotary engine often suffers incomplete combustion and high emissions at idle and low speed and load due to the high residual gas and low combustion temperature. Therefore, experiments in this paper were concentrated at idle and low speed and load conditions of the rotary engine.Firstly, experiments on combustion and emissions characteristics of a hydrogen-blended gasoline rotary at idle was conducted. The engine speed was set to around 2400 r/min. The hydrogen volume fraction in the intake was raised from 0 to 6.8% by changing the hydrogen injection duration. For each volume fraction in the intake, the gasoline injection duration was adjusted by the HECU to keep the mixtures global excess air ratio at the stoichiometric. The results showed that the coefficient of variation in speed and fuel energy flow rate were simultaneously decreased after the hydrogen blending. The flame development and propagation periods were shortened after the hydrogen enrichment. The maximum combustion temperature was enhanced with hydrogen addition. The exhaust temperature and cooling loss were decreased when the hydrogen volume fraction in the intake was increased. The hydrogen addition in the intake was effective on reducing HC, CO and CO₂ emissions. NOx emissions were small due to the low combustion temperature of the rotary engine. No clear effect of hydrogen addition on NOx emissions was found in this test.Then, the effect of hydrogen addition on combustion and emissions characteristics of a gasoline rotary engine at the part load condition was investigated on the testing bench. The gasoline rotary engine was operated at a constant speed of 3000 r/min and a manifolds absolute pressure of 37.5 k Pa with the stoichiometric excess air ratio. The spark timing was set at 25 °CA before top dead center. The hydrogen volume fraction in the intake was gradually increased from 0 to 5.2%. The results showed that the combustion pressure, brake mean effective pressure and brake thermal efficiency were simultaneously increased after the hydrogen blending. The crank angle relevant to the peak chamber pressure was advanced with hydrogen addition. The hydrogen enrichment was effective on reducing the flame development and propagation periods. The maximum combustion temperature was increased due to the hydrogen addition. The exhaust temperature and cooling loss were decreased after the hydrogen enrichment. The coefficient of variation in flame propagation period was decreased after hydrogen blending. HC emissions were reduced by 44.8% when the hydrogen volume fraction in the intake was raised from 0 to 5.2%, CO and CO₂ emissions were also reduced after the hydrogen blending. NOx emissions were slightly increased when hydrogen was blended.