A study of homogeneous ignition and combustion processes in CI, SI, and HCCI engine systems

Emissions remain a critical issue affecting engine design and operation, while energy conservation is becoming increasingly important. One approach to favorably address these issues is to achieve homogeneous charge combustion at lower peak temperatures with a high compression ratio – the goal of Homogeneous Charge Compression Ignition (HCCI) engines. This thesis focuses on developing appropriate kinetic models for HCCI engines and on experimentally exploring new paths to address the limitations with current and advanced technologies.Since fuel oxidation chemistry determines HCCI engine performance, a model describing fuel oxidation at these conditions would be a useful design tool. HCCI engine experiments were conducted to provide the essential database for modeling, including temperature, pressure, ignition delay, and heat release. An existing pre-ignition skeletal chemical kinetic model was applied to HCCI ignition. Then, it was improved and extended to cover the entire HCCI combustion process. A global reaction model also was constructed for CFD simulations. Simulations using these models are generally in good agreement with the experimental data.During our investigations into HCCI and autoignition processes, we have observed some ignitions that begin at much lower temperature (< 550 K) than expected. This is at odds with the generally accepted explanation of autoignition in HCCI engines, that the reactivity is driven by temperature, where autoignition occurs after the mixture has reached some critical temperature (approx. 1000 K). We have attempted to investigate the origins of these lower temperature autoignition phenomena, and we propose that traditional models may be missing the low temperature chemistry that explains this behavior. Our analysis indicates that proper utilization of these lower temperature phenomena may provide a means to better control SI, CI, and HCCI engines.Finally, to develop a better understanding of the autoignition chemistry of fuel mixtures and blends, this study investigated the preignition behavior of nheptane, iso-octane, and propionaldehyde blends in a pressurized flow reactor. Experimental results indicated that the effect of fuels in blends can be interpreted in terms of their radical scavenging behavior. To be effective as a scavenger, a fuel must have an overlapping reactivity range and a lower reactivity than the other fuel.Ph.D., Mechanical Engineering -- Drexel University, 200