Ignition Phenomena in the Chalmers High Pressure High Temperature Spray Rig

It is known that there exists a time period between the instant when the conditions for combustion are settled and the start of combustion, this induction stage is called ignition delay. The ignition delay is important for the control of diesel engines. However, in the Chalmers High Pressure High Temperature (HP/HT) spray rig it has been observed that the ignition delay varies from injection to injection. This study was performed to investigate the variation of ignition delay as a function of gas pressure, gas temperature, injection pressure and injection duration. Diesel fuel was injected into the Chalmers HP/HT rig containing hot and pressurised air using a common rail injection system. Pressure and temperature in the combustion chamber were controlled and varied as well as the injection pressure using medium or long injections. The spray combustion was filmed using a high speed camera and the ignition delay was measured with a photodiode taking as a threshold of start of ignition the beginning of light emission by the flame. The control pulse given to the injector, the needle lift and the photodiode signal were controlled, registered and measured by a computer. The ignition delay measurements showed a variation of the ignition delay between injections. The statistical data from the ignition delay measurements showed a variation of the mean, standard deviation and probability density functions of the ignition delay for different operational conditions