Study On The Simultaneously Acquisition System Of Cylinder Pressures For Multi-Cylinder Spark Ignition Engines

The developing and debugging process of 'the simultaneously acquisition system of cylinder pressures for multi-cylinder spark ignition engines' were introduced in detail in this thesis. The experimental results of 492QC and 492WQB engine using this acquisition system were introduced too.The measurement system consist of computer, 16-channel high speed data acquisition board, spark plug pressure sensor, crank angle signal generator, charge amplifier and oscillograph. The max acquisition frequency of this system is 1MHz. There are 4 chips of AD684 on the data acquisition board. The most permissible input signals are 16-channel simultaneously. The frequency of sampling, the number of signals and the total data quantity can be controlled by the program made for this acquisition system. The pressure sensor is Kistler 6117A46 spark plug piezoelectric pressure sensor. The pressure sensor is integrated with the spark plug so we do not need drilling another hole on the cylinder head and avoid changing the structure of combustion chamber and the effect of connecting channel on the measured cylinder pressure. The all cylinder's pressure for any cycle can be recorded continuously and simultaneously using this system. This is very important for the research of engine's transient working condition and the pressure fluctuation among each cylinders and different cycles of the same cylinder.This cylinder pressure simultaneously acquisition system can be extended easily. The signals of -5V-- +5V can be measure by modifying the sampling program. The air-fuel ratio was measured continuously as an example.The cylinder pressures of engines type 492QC, 492WQB were measured continuously and simultaneously under motoring condition. The S.I. engine was motored by a 37kW electric engine and the S.I. engine's revolution was change by a 4-position transmission. At lease 30 cycle'spressure data of each cylinder were measured. These cycle's pressure of each cylinder were averaged by the program that we made and the fluctuant coefficient of pressure was calculated. The comparison among each cylinder's quantity of inlet air was made using the average value of the max pressure of each cycle.The combustion pressures of each cylinder were measured continuously and simultaneously of the engine 492QC burning gasoline and CNG. The comparisons of combustion and fluctuant among each cylinder were made using the averaged value of the max pressure and the fluctuant coefficient of the max pressure. And the experimental results indicated that the pressure fluctuant of CNG engine was less than gasoline engine.