Research On The Particle Emission Characteristic During Warm Up Processes Of GDI Engine

With the development of technology and the improvement of the traffic facilities, vehicle has become an important travel tools in people’s lives. In 2015, China had become the largest country in the global market and there was exceeding 24 million cars has been sold and produced, but that also brought a series of problems such as the lack of energy and environmental pollution problems. Energy shortages directly restrict China’s economic and social sustainable development, which also hinder the realization of the Chinese dream. Environmental pollution harm people’s health directly and hamper the harmonious development for human and nature. With the increasingly strict emission regulations and automotive technology mature, GDI technology more widely applied in automobile market.GDI technology has better fuel economy and power performance, but in the process of cold start and warm up which has higher particle emissions. In order to seek more optimized control strategy and improve the combustion efficiency as well as reduce particulate emissions, this paper had a research about particulate emissions for warm up process of GDI engine.Based on the project from National Natural Science Foundation "The effect of wall fuel film of cold start and warm up on unburned HC and particle in GDI engine", We research on the effect of operation parameters on the combustion and particle emission characteristics. The early stage of the main work includes the set up of GDI engine test bench and designs a 2 stage heat dilution sampling system, furthermore an engine control hardware and software have been accomplished. Through ECU which is designed by our researching team can controls engine operation parameters real-time.Firstly we researched the effect of the excess air ratio, ignition timing, injection pressure on combustion condition for the warm-up process of GDI engine, which was analyzed by the change of the cylinder pressure, instantaneous heat release rate and the exhaust temperature. Secondly we researched the effect of the excess air ratio, ignition timing, injection pressure on particle emission for the warm-up process of GDI engine, which was analyzed by the change of THC emissions, particle number concentration and volume concentration. The main research conclusion of this paper has the following points;1. When the different excess air ratio were used for warming up, the air ratio increased from 0.8 to 1.2 which lead to the cylinder pressure and instantaneous peak heat release rate first rise and then reduce and the peak phase firstly move forward and then backward, With the improvement of cooling water temperature that had the same change trend. In excess air ratio of 0.9, cylinder pressure and heat release rate was the highest peak. Under the same cooling water temperature, with the excess air ratio increased exhaust temperature first increase and then reduce. Exhaust temperature was highest when excess air ratio was 0.9.THC concentration was highest when excess air ratio is 0.8.With the improvement of cooling water temperature, the THC concentration was reduced. When excess air ratio increased from 0.8 to 1.2, distribution of the particle number concentration gradually changed from accumulation unimodal to nuclear unimodal. Rich mixture and high cooling water temperature was beneficial to generate the accumulation particle, whereas to generate nuclear particle. When excess air ratio is 1.0 ~ 1.2, the total particle number concentration was low. When different excess air ratios were used for warming-up, all the particles volume concentration are unimodal distribution.When excess air coefficient was 1.0 ~ 1.2, the total volume concentration was two orders of magnitude less than the rich mixture. From the combustion state analysis, excess air ratio 0.9 was used for warming up as the burning in cylinder was better. From the THC emissions and particulate emissions analysis, excess air ratio 0.9and 1.0 were better for warming up as THC and particulate emissions were fewest.2. With the advance of ignition timing, maximum combustion cylinder pressure gradually increased and the peak phase gradually forward. Under the same ignition timing, the highest peak combustion pressure and heat release rate increased and the peak phase moveed forward with the increase of cooling water temperature. With the advance of ignition timing, exhaust temperature was reduced and the concentration of THC gradually increased. The cooling water increased from 35 ℃ to 85 ℃ that led to the THC decreased 82 ppm. With the advance of ignition timing, particle number concentration gradually changed from unimodal distribution to bimodal distribution and particle volume concentration was still unimodal distribution. Under Ignition timing before 18 ° CA BTDC and cooling water temperature at 45 ℃, the number of total concentrations was highest. After 18 ° CA BTDC, the total number of concentration decreased with the improvement of temperature. Nucleation mode particle number concentration and the total number of concentration had the same change trend. With the advance of ignition timing, total volume concentration, nucleation mode volume concentration and accumulation mode volume concentrations were higher. Based on the analysis of the data, combustion in cylinder was best when the ignition timing was 32 ° CA BTDC. When the ignition timing was 11 ° CA BTDC, exhaust temperature was highest, but THC and volume concentration and particle emissions was least.3. When the different injection pressures were used for warming up, cylinder pressure peak and the instantaneous peak heat release rate first increased and then decreased with the increase of injection pressure, as well as the cylinder pressure peak phase moved first forward and then backward, but heat release rate peak phase moved backward. When the injection pressure was 5 MPa, the cylinder pressure and maximum instantaneous heat release rate were highest. With the increase of cooling water temperature, cylinder pressure peak and the peak heat release rate increased and the peak phase moves forward. Although injection pressure have less effected on the exhaust gas temperature in the process of warming up, it greatly influenced by the cooling water temperature. When the injection pressure was 7 MPa, the THC concentration was the highest. THC concentration was the lowest in 5 MPa injection pressure.With the increase of cooling water temperature, the THC concentration was reduced.When different injection pressure were used for warming up, particle number concentration presented the bimodal distribution and particle volume concentration presented unimodal distribution; With the increase of injection pressure, particle total number of concentration and total volume of concentrations were increased. By the above analysis, when the injection pressure was 5 MPa, the combustion was best and exhaust temperature was highest simultaneously. At the same time, THC, the number of particles concentration and the volume concentration were least.