Correlation of Performance, Exhaust Gas Temperature and Speed of a Spark Ignition Engine Using Kiva4

The objective of this study was to investigate performance characteristics of a spark ignition engine, particularly, the correlation between performance, exhaust gas temperature and speed, using Kiva4. Test data to validate kiva4 simulation results were conducted on a 3-cylinder, four-stroke Volkswagen (VW) Polo 6 TSI 1.2 gasoline engine. Three different tests were, therefore, carried out. In one set, variations in exhaust gas temperature were studied by varying the engine load, while keeping the engine speed constant. In another test, exhaust gas temperature variations were studied by keeping the engine at idling whilst varying the speeds. A third test involved studying variations in exhaust gas temperature under a constant load with variable engine speeds. To study variations in exhaust gas temperatures under test conditions, a basic grid/mesh generator, K3PREP, was employed to write an itape17 file comprising of a 45° asymmetrical mesh. This was based on the symmetry of the combustion chamber of the engine used in carrying out experimental tests. Simulations were therefore performed based on the input parameters established in the conducted tests. Simulations with the kiva4 code showed a significant predictability of the performance characteristics of the engine. This was evident in the appreciable agreement obtained in the simulation results when compared with the test data, under the considered test conditions. A percentage error, between experimental results and results from simulations with the kiva4 code of only between 2% to 3% was observed.

Experimental Investigation for NO_x Emission Reduction in Hydrogen Fueled Spark Ignition Engine Using Spark Timing Retardation, Exhaust Gas Recirculation and Water Injection Techniques

The experimental tests were carried out on a single cylinder hydrogen fueled spark ignition(SI)generator set with different spark timings(4-20℃A bTDC),exhaust gas recirculation(EGR)up to 28% by volume and water injection up to 1.95 kg/h(maximum water to fuel mass ratio of 8:1).The engine speed was kept constant of 3000 r/min.The NOx emission and thermal efficiency of engine with gasoline and hydrogen fuel operation at 1.4 kW power output are 5 g/kWh and 12.1 g/kWh,and 15% and 20.9% respectively.In order to reduce the NOx emission at source level,retarding spark timing,exhaust gas recirculation(EGR),and water injection techniques were studied.Nox emission decreased with spark timing retardation,EGR,and water injection.NOx emission with hydrogen at 1.4 kW power output decreased from 12.1 g/kWh with maximum brake torque(MBT)spark timing(10℃A bTDC)to 8.1 g/kWh with retarded spark timing(4℃A bTDC)due to decrease in the in-cylinder peak pressure and temperature.The Nox emission decreased to 6.1 g/kWh with 20% EGR due to thermal and chemical dilution effect.However,thermal efficiency decreased about 33% and 17% with spark timing retardation and 20EGR respectively as compared to that of MBT spark timing.But,in the case of water injection,the NOx emission decreased significantly without affecting the thermal efficiency of the engine and it is 5.6 g/kWh with water-hydrogen ratio of 4:1(water flow rate of 0.92 kg/h).Water injection is the best suitable method to reduce the NOx emission in a hydrogen fueled engine compared with the spark timing retardation and EGR technique.

提高SI燃烧废气稀释极限

针对不同负荷之间,均质充量压燃着火和传统火花点燃两种燃烧模式的转换问题,在HCCI燃烧的边界外SI工况点上,通过内外部废气耦合控制燃烧结合气门参数调整的方法,在一台装有全可变气门机构的单缸进气道喷射实验发动机上,进行了拓展SI燃烧废气稀释极限的研究.目的是减少两种燃烧模式之间的热阶跃和稀释度阶跃,以实现无缝的负荷调节.研究发现:通过调整不同的内外部废气比例,结合气门参数的调节,可以有效拓展SI燃烧的废气稀释极限,从5%左右提升至30%左右,同时得到较好的燃油经济性.与此同时,气门参数的设定也可以与HCCI相接近,减少了两者气门参数之间的差距.但是在优化过程中,必须要规避由于热振荡现象造成的循环变动限制.

辅助火花点火对DME微引燃汽油稀释复合燃烧的影响

DME(dimethylether,二甲醚)微引燃汽油稀释复合燃烧模式,可以实现汽油机高效低温燃烧.但是在DME总热值比受限条件下,废气稀释存在极限条件,限制了经济性的进一步提升.为提高稀释燃烧经济性,采用火花点火可以提升集聚型DME微引燃相对燃烧速度,可以提高离散型DME微引燃绝对燃烧速度.研究结果表明:火花点火对两种微火源引燃都具有促进作用,在离散型微火源策略中采用火花点火对经济性提升更明显,相对于火花点火辅助集聚型微引燃可提高3.88%.