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Technical Paper

Optical Experiments on Strong Knocking Combustion in Rapid Compression Machines with Different Fuels

Nowadays the strong knocking combustion involving destructive pressure wave or shock wave has become the main bottleneck for highly boosted engines when pursuing high thermal efficiency. However, its fundamental mechanism is still not fully understood. In this study, synchronization measurements through simultaneous pressure acquisition and high-speed direct photography were performed to comparatively investigate the strong knocking combustion of iso-octane and propane in a rapid compression machine with flat piston design. The pressure characteristics and visualized images of autoignition and reaction wave propagation were compared, and the correlations between thermodynamic trajectories and mixture reactivity progress were analyzed. The results show that iso-octane behaves a greater propensity to strong knocking combustion than propane at similar target pressures.
Technical Paper

Knock Threshold Detection in Turbocharged Gasoline Engine Using EEMD and Bispectrum

Knock threshold detection is the key of closed loop control of ignition in gasoline engine, and it is also the difficult point in knock measurement. In this paper, an investigation of knock detection in turbocharged gasoline engine using bispectrum slice and ensemble empirical mode decomposition (EEMD) based on the engine cylinder head vibration signals is presented. By adding some finite amplitude Gaussian white noises to the signal, EEMD keeps the signal continuous in different time span, and therefore the mode mixing inhering in the classical empirical mode decomposition (EMD) method is alleviated. Power spectrum density (PSD) estimation is used to determine the band range of the resonance frequency generated by knock component. EEMD is used to decompose the original signals, the time-frequency characteristics of the Intrinsic Mode Functions (IMF) are analyzed using Continues Wavelet Transform (CWT) due to its excellent time-frequency resolution.
Technical Paper

Pump-End Control Technology for Small Engine Management System

A pump-end control technology for pump-nozzle fuel supply unit, in which the pump is driven and controlled electrically for pressurizing and metering the fuel fed into an engine, is studied. The unit is composed of a solenoid driven plunger pump, a high-pressure fuel tube, and an auto-open nozzle, and only the pump is propelled by PWM power from an ECU. To achieve a higher metering accuracy, a metering theory deciding the fuel discharging rate was developed by studying the system using a physical-mathematical model. The developed so called T3 theory makes the fuel supply unit with excellent metering consistency under various conditions, which can meet the requirement of fuel supply unit application to small engine management system. The study reveals that an electrically characterized variable, T3, which is associated with the net output energy, can directly results in a mass discharge.
Technical Paper

An Investigation of Abnormal Spray Behaviors of Multi-Hole GDI Injector

The main objective of this paper is to investigate the influence of injection pressures and fuel temperatures on the secondary injection spray evolution at the end of injection from a multi-hole gasoline direct injection (GDI) injector by Mie-scattering technique. The results of this paper show that the overall injection process can be classified into five stages which are injection delay stage, main injection stage, dwell stage, secondary injection stage and ligaments breakup stage respectively. Especially, the secondary injection occurs at the end of main injection, which is abnormal and undesirable spray behaviors. During the injection, big droplets and ligaments are injected through nozzle orifices at low speed. As the injection pressure increases, the phase of the secondary injection advances, and the injection duration decreases. At medium injection pressures (at 6, 8 MPa), more quantity of fuel are injected as ligaments.