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Research has been conducted on an extended expansion engine, using a multiple linkage system to increase the thermal efficiency of general-purpose engines. A four-jointed linkage was used between the connecting rod and the crank pin of a standard piston-crank system. The end of the linkage rotates at half the speed of the crankshaft, resulting in piston strokes unequal length in each revolution. The length of the expansion stroke is greater than that of the compression stroke, thereby providing an extended expansion cycle. This thermal cycle is just Atkinson cycle, and precisely different from Miller cycle, which often required supercharging or variable valve timing control system. Theoretical thermal efficiency and numerical simulations were used to determine the increase in thermal efficiency at a compression ratio of 8.5 and an expansion ratio of 12.3.

In recent years, improvements in the fuel economy and exhaust emission performance of internal combustion engines have been increasingly required by regulatory agencies. One of the salient concerns regarding general purpose engines is the larger amount of CO emissions with which they are associated, compared with CO emissions from automobile engines. To reduce CO and other exhaust emissions while maintaining high fuel efficiency, the optimization of total engine system, including various design parameters, is essential. In the engine system optimization process, cycle simulation using 0-D and 1-D engine models are highly useful. To define an optimum design, the model used for the cycle simulation must be capable of predicting the effects of various parameters on the engine performance. In this study, a model for predicting the performance of a general purpose SI (Spark Ignited) engine is developed based on the commercially available engine simulation software, GT-POWER.

Two of the goals of the Penn State FutureTruck project were to reduce the emissions of the hybrid electric Ford Explorer to ULEV or lower, and improve the fuel economy by 25% over the stock vehicle. The hybrid electric vehicle system is powered with a 103kW 2.5L Detroit Diesel engine which operates with a fuel blend consisting of ultra-low-sulfur diesel and biodiesel (35%). Lower emissions are inherently achieved by the use of biodiesel. Additionally, the engine was fitted with a series of aftertreatment devices in an effort to achieve the low emissions standards. Vehicle testing has shown a gasoline-equivalent fuel economy improvement of approximately 22%, a reduction in greenhouse gas emissions by approximately 38%, and meeting or exceeding stock emissions numbers in all other categories through the use of an advanced catalyst and control strategy.

The purpose of this study was to investigate how autoignition leads to the occurrence of pressure oscillations. That was done on the basis of in-cylinder visualization and analysis of flame images captured with a high-speed camera using an optically accessible engine, in-cylinder pressure measurement and measurement of light emission from formaldehyde (HCHO). The results revealed that knocking intensity tended to be stronger with a faster localized growth speed of autoignition. An investigation was also made of the effect of exhaust gas recirculation (EGR) as a means of reducing knocking intensity. The results showed that the application of EGR advanced the ignition timing, thereby reducing knocking intensity under the conditions where knocking occurred.

Research on extended expansion engine was carried out in order to enhance thermal efficiency in general purpose engines. A four-jointed linkage was used between the connecting rod and the crank pin of a standard piston-crank system and provides an Atkinson thermo dynamic cycle. Thermal efficiency of an engine with a compression ratio of 12.4 and an expansion ratio of 18.1 was compared to an engine with a compression ratio of 9.4 and an expansion ratio of 13.6. Measured indicated thermal efficiency of prototyped engine operated by natural gas was 38.7%, a 2.6% increase, as predicted in the numerical simulation.