Development of a Rate of Injection Bench and Constant Volume Combustion Chamber for Diesel Spray Diagnostics

To help understand the complex fuel spray combustion phenomena in modern diesel engine using high injection pressure, a fuel injection test bench and a constant volume combustion chamber were developed and demonstrated in this study for diesel spray diagnostics. Both facilities are significant when linking between spray injection and combustion dynamics and engine performance. This link is important to determine changes needed in order to optimize the performance of a diesel engine. Combustion and emissions of a diesel engine are influenced by the rate of fuel injection which, in turn, is determined by the injection pressure, nozzle geometry, and fuel type. The rate of injection bench capable of studying a modern common-rail injection system was designed, fabricated, and demonstrated in this study. Experimental apparatus included a high pressure fuel pump, a fuel rail, a transient pressure transducer, and a data acquisition and control system. The rates of injection of different injectors with various nozzle diameters and spray angles injecting different types of fuel under different injection schemes were investigated. Results of this study showed that for the same injector, the differences in the rates of injection were negligible under the same injection conditions with variations only in the back pressure from 2.07 MPa to 6.21 MPa. When injection pressure was increased from 75 MPa, to 100 MPa, and to 150 MPa more fuel was injected and the rise and decay of the injection rate also increased. This indicated that fuel exited the nozzle at a faster rate. Subsequently, as injection pressure was increased, a higher peak injection rate was seen. If the same fuel quantity was desired, injection duration was shortened. When comparing the rate of injection for diesel and biodiesel blend (i.e, B20 and B100), the rates of injection were comparable but the injected mass of biodiesel was slightly higher because biodiesel has a slightly higher density. On the other hand, the difference in the delay between the electronic injection signal and the onset of injection was negligible for diesel and biodiesel blends using the current common-rail system. Additionally, the rate of injection for the double injection scheme was also studied and results showed that the shape of individual injection in the multiple injection schemes was similar to that of single injection. To further understand the engine in-cylinder combustion process, a constant volume combustion chamber was also developed and demonstrated in this study. With optical access provided by quartz windows, experiments using modern laser imaging and spectroscopy were performed to further understand high-speed diesel fuel jet development. The previous experiment was revisited using a superior camera to capture higher quality images to study the diesel spray structure. The previous constant volume heated chamber was then converted to a constant volume pre-combustion chamber. During this conversion, seals were redesigned and new O-rings seals were utilized. In addition, a high speed mixing fan, powerful ignition system, and data acquisition and control system were implemented. After the conversion, it was demonstrated that the new combustion chamber could attain temperature up to 919 K while showing negligible leaks. Even higher temperature and pressure could be attained if more combustible gas mixture was inputted. The combustion chamber developed in this study can be readily utilized to study high-speed diesel jet combustion under high-pressure and high-temperature environments