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Downsizing is an important concept to reduce fuel consumption as well as emissions of spark ignition engines. Engine displacement is reduced in order to shift operating points from lower part load into regions of the operating map with higher efficiency and thus lower specific fuel consumption [ 1 ]. Since maximum power in full load operation decreases due to the reduction of displacement, engines are boosted (turbocharging or supercharging), which leads to a higher specific loading of the engines. Hence, a new combustion phenomenon has been observed at high loads and low engine speed and is referred to as Low-Speed Pre-Ignition or LSPI. In cycles with LSPI, the air/fuel mixture is ignited prior to the spark which results in the initial flame propagation quickly transforming into heavy engine knock. Very high pressure rise rates and peak cylinder pressures could exceed design pressure limits, which in turn could lead to degradation of the engine.

A technique was developed for measuring the Laminar Burning Velocity (LBV) of multi-component fuel blends for use in high-performance spark-ignition engines. This technique involves the use of a centrally-ignited spherical combustion chamber, and a complementary analysis code. The technique was validated by examining several single-component fuels, and the computational procedure was extended to handle multi-component fuels without requiring detailed knowledge of their chemical composition. Experiments performed on an instrumented high-speed engine showed good agreement between the observed heat-release rates of the fuels and their predicted ranking based on the measured LBV parameters.

Increasingly stringent emissions regulations require that modern diesel aftertreatment systems must warm up and begin controlling emissions shortly after startup. While several new aftertreatment technologies have been introduced that focus on lowering the aftertreatment activation temperature, the engine system still needs to provide thermal energy to the exhaust for cold start. A study was conducted to evaluate several engine technologies that focus on improving the thermal energy that the engine system provides to the aftertreatment system while minimizing the impact on fuel economy and emissions. Studies were conducted on a modern common rail 3L diesel engine with a custom dual loop EGR system. The engine was calibrated for low engine-out NOx using various combustion strategies depending on the speed/load operating condition.

Southwest Research Institute, as part of the Clean Diesel IV consortium, built a multi-cylinder HCCI engine that ran in the HCCI combustion mode full-time. The engine was used to develop HCCI fuels, demonstrate the potential operating range of HCCI, and to demonstrate the feasibility of transient control of HCCI. As part of the engine design, a hardware based method of decoupling control of air and EGR was developed and patented [ 1 ]. The system utilized a positive displacement supercharger with a controlled bypass valve for air-flow control, and a high-pressure loop EGR system with variable geometry turbocharger to control the EGR rate. By utilizing the system, the required precision from the air and EGR control in the engine controller was reduced.

A series of tests using an open beam laser ignition system in an engine run on pre-mixed, gaseous fuels were performed. The ignition system for the engine was a 1064 nm Nd:YAG laser. A single cylinder research engine was run on pre-mixed iso-butane and propane to determine the lean limit of the engine using laser ignition. In addition, the effect of varying the energy density of the ignition kernel was investigated by changing the focal volume and by varying laser energy. The results indicate that for a fixed focal volume, there is a threshold beyond which increasing the energy density [kJ/m3] yields little or no benefit. In contrast, increasing the energy density by reducing the focal volume size decreases lean performance once the focal volume is reduced past a certain point. The effect of ignition location relative to different surfaces in the engine was also investigated. The results show a slight bias in favor of igniting closer to a surface with low thermal conductivity.