Effects Of Fuly Variable Valve System On Intake And Combustion Performance Of SD2100TA Diesel Engine

Lower compression ratio is necessary for diesel engine to improve indicated thermal efficiency at small and medium loads, and higher compression ratio is essential to decrease peak pressure indicated thermal efficiency at full load, hence the application of miller cycle on diesel engine faces huge potential. So the Variable Valve Timing (VVT) technology has been focused on during recent years. Some new clean combustion modes such as Homogeneous Charge Compression Ignition (HCCI), Premixed Charge Compression Ignition (PCCI) and Low temperature Combustion (LTC) were put forward to avoid the formation region of pollutants. The combination of pressure boost, Exhaust Gas Re-circulation (EGR) and VVT are applied to achieve the control of equivalence ratio, cylinder temperature and optimum combustion. Compared with the EGR, VVT response more quickly and is achieved more easily. In brief, VVT has important effects on diesel engine.To investigate the effects of VVT on diesel engine, a fully hydraulic variable valve actuation using Early Intake Valve Closing(EIVC) mode was developed and assembled on a SD2100TA diesel engine. The continuous variability of the maximum valve lift, opening duration and timing were attained. The intake mass flow and effective compression ratio could be adjusted in large range. Experiments were conducted under torque of 25N·m,50N·m,75N·m, Intake Valve Closing Timing (IVCT) of 30°CA ATDC、-4°CA ATDC、-27°CA ATDC and -50°CA ATDC, engine speed of 1200r/min and 1650r/min, fuel supply angle of 20CA BTDC、24CA BTDC、27CA BTDC. Some parameters such as cylinder pressure, BSFC and exhaust temperature were recorded.The results indicate that the intake and combustion performance are greatly affected by EIVC, which are concluded as three aspects as follows:(1) Compared with throttle valve control mode, pumping loss is reduced substantially and cylinder mean temperature is decreased by EIVC mode, which is beneficial for Low Temperature Combustion (LTC). Intake temperature of throttle case is increased by 31℃ at BDC with the intake mass flow of 36.7kg/h.(2) With the advance of Intake Vale Closing Timing (IVCT), the effective compression ratio is decreased, the cylinder pressure and temperature at the end of compression stroke are lowered, the ignition delay is increased, the start of heat release is delayed, the proportion of premixed combustion is increased, the proportion of diffusion combustion is decreased, and the exhaust temperature is decreased because of reduction in heat capacity.(3) A significant reduction in peak pressure is obtained with fixed indicated thermal efficiency. The peak pressure is decreased from 7.87Mpa to 5.8Mpa, reduced by 26%, at 1650r/min and BMEP of 0.5 Mpa while IVCT is advanced from 30°CA ABDC to -50°CAABDC.