| In recent years,China's automobile industry has ushered the peak of development with the continuous improvement of economic and urbanization,the automobile amount in big cities increases annual,accompanied by the increasing energy and environmental pressures,the urban traffic has become more crowed.Hybrid electrical vehicles(HEV)have good energy saving and environmental protection because they are drove by oil and electricity.Stop/re-start technology is an important fuel-saving method of HEV.Engine for HEV application usually adopts quick start.Cranking speed of the quick start is high,which will cause strong transient characteristics during starting process;injected fuel in the initial cycles should be enriched,these will cause deterioration of in-cylinder combustion and emissions.For improving starting performance,it is necessary to study the engine quick start characteristics.Compare idle and stop/re-start strategies,energy consumption and emissions of stop/re-start strategy will be greater than those of idle strategy will be for a short parking.Therefore,it is necessary to calculate the minimum time to choose stop/re-start strategy based on energy consumption and emissions.In addition,alcohol fuels ideal alternative fuel.If engine for HEV application fueled with alcohol fuels,the energy saving and environmental characteristics may be further improved.This article will experimental study the idle and re-start performance of engine fueled with alcohol fuels.To study experimentally,a testing bench of engine for HEV application was built,control software for testing equipment was developed.To achieve idle and re-start of HEV engine,idle and re-start control strategies were self-developed based on MATLAB/Simulink.The idle control strategy was PI closed-loop control and the re-start was cycle-by-cycle control.The fuel injected mass was calibrated based on engine speed,intake pressure and coolant temperature.The idle characteristics with different fuels was experimentally studied,and the experiments were based on coolant temperatures and idling speeds.The results show with the coolant temperature rose,the energy consumption per cycle decreased,combustion periods and COVimep increased,HC,CO2 and NOx emissions reduced;with the idling speed increased,the energy consumption per cycle,combustion periods and NOx emissions increased,COVimep,HC and CO2 emissions decreased.Alcohol fuels could improve idle performance significantly;the fuel economy,combustion and emissions characteristics in idle of engine with alcohol fuels were improved.The quick start characteristics of engine used for HEV were experimentally studied based on motor cranking speed,spark advance,coolant temperature and fuels.The main results showed as follows: engine starting transient characteristics could be weakened by increased motor cranking speed to around target idling speed,which led to low energy consumption,HC and NOx emissions.With increase of spark advance,in-cylinder pressure in first cycle rose,max of HC emissions and exhausted temperature lowed,but max of NOx emissions also increased.The energy consumption,HC and NOx emissions were increased with the decreased of the coolant temperature.Experiments of quick start with alcohol fuels were conducted.The results showed that the fuel economy,combustion and emissions characteristics in quick start of engine with alcohol fuels were improved.Parking strategy of engine for HEV application was optimized based on energy consumption and emissions.From energy consumption,HC and NOx emissions,the best quick start speed was 1000 rpm.For 1000 rpm quick start,the optimized results based on energy consumption,HC and NOx emissions showed,the minimum parking time to choose stop/re-start strategy is 4.5s,7.0s and 2.7s,respectively.From a comprehensive perspective,the minimum parking time to choose stop/re-start strategy of gasoline engine should be more than 7.0s.In addition,alcohol fuels could reduce the minimum parking time to choose stop/re-start strategy. |
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