Simulation Research On The Effect Of Combustion For Low Emission NG Engine With Dual-Spark-Ignition

Natural gas has a wide application prospect in the market because of the traditional energy crisis growing, and as an alternative fuel for vehicle has many advantages. Compressed natural gas(CNG) engine can match with Three Way Catalysts(TWC- Postprocessor of high conversion efficiency and low cost) to meet the stringent emission regulations with stoichiometric air-to-fuel ratio combustion model. The problem of this combustion model is the heat load and detonation tended become more higher and easier, at the same time the flame propagation of CNG fuel is slow, which reduce the CNG engine efficiency. Therefore, this article adopts the big EGR rate to reduce the heat load under heavy load and Dual-Spark-Ignition to realize the rapid combustion as the technical route under λ=1.First of all, using GT-POWER software build the one-dimensional simulation platform for CNG engine, and study the influence law of different EGR rate on the engine performance, and it is concluded that achieve maximum EGR rate under low and high load. After that, adopting AVL-FIRE 3-D simulation software to study objectively the combustion process of the maximum EGR rate under heavy load combined double spark plug ignition technology, and obtained the effect law of different ignition strategy and energy on engine performance.Based on the 1-D simulation platform established by GT-POWER software and the condition of 25% and 75% load, theoretical air-fuel ratio, n=2840r/min, research the influence law of different EGR rate on the CNG engine performance. Results show that with the increase of EGR rate, the peak combustion pressure in cylinder and heat release rate curve become lower and move backward; only reach a certain amount can cold EGR lower the temperature in cylinder, EGR rate is 15% can’t have the effect of reducing heat load at low load, and until 17% EGR rate could make the temperature began to decline, more than 20% let the heat load in engine be controlled within 700℃ in high load; CNG fuel burned in the condition of theoretical air-fuel ratio, the generation of CO in high load(75%) can be reduced and in low load(25%) can be more, both can well control the amount of NOx and increase the amount of HC; Simulation results provide the objective research for experiment, the economy of CNG engine is bad with the increase of EGR rate, and there is a certain development space(using double spark plug –the rapid combustion technology to improvement the economy) is developed; it is not suitable for pumping in EGR in cylinder under low load.Simulation results based on the 1-D platform and laws, and in virtue of CFD software research the qualitative and quantitative analysis of combustion process and performance about CNG engine in terms of different ignition strategies between single and double spark plug and the optimal spark advance angle respectively and ignition energy under stoichiometric combustion and 75% load and 25% EGR rate. The results show that the double spark plug can shorten the flame propagation distance, and improve the speed of CNG flame propagation effectively. The reasonable ignition timing would develop the performance of CNG engine to the best for single and double spark plug ignition strategies when EGR rate equal 25%, the best ignition timing of the single spark plug for near 655 ° CA(65°CA-BTDC), double synchronous ignition spark plug is 665 ° CA(55°CA-BTDC), double asynchronous spark plug ignition is 665-660 ° CA(55-60°CA-BTDC); Under the best ignition performance, double ignition combustion duration than single spark plug shortened about 20 ° CA; The strategy of double spark plug ignition heat load is higher than single spark plug strategy; Ignition timing to the degree of the influence of different ignition strategy : the biggest effect is single spark plug, second is double synchronous spark plug ignition, minimum impact is double asynchronous spark plug ignition. Double spark plug ignition increase 2KW indicated power compared with single spark plug, improve indicated fuel consumption by about 8%, significantly improve the quality of performance and combustion for CNG engine; Based on double synchronous at 665 ° CA ignition spark plug, and the initial ignition energy of 35 m J, 45 m J, 55 m J, 65 m J proceed CNG engine performance analysis, according to the influence of the comparative study of fire nuclear radius, cylinder pressure, heat release rate, average temperature, NO generation and combustion characteristic parameters and indicated performance indicators generated from different initial ignition energy in synchronous ignition, in the case of ensuring normal ignition, initial ignition energy has little influence to combustion process of charge in cylinder when on going into the high EGR rate and the condition of theoretical air-fuel ratio(lambda = 1).