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A variable stroke engine was proposed as a promising solution for improving the efficiency of flex-fuel engines by adjusting the compression ratio; this prevents knock onset for fuels with different octane numbers. Similarly, the displacement was adjusted by varying stroke length with the objective of mitigating cylinder pumping losses. This article compares the efficiency of a spark-ignition, port-fuel injection engine, with variable displacements and compression ratios; a conventional engine with a fixed compression ratio; and an engine with variable compression ratios. A simulation-based calibration was performed for each engine, using the results from a phenomenological model to predict the engine performance. The calibration maps were obtained by maximising efficiency through determining the optimal combination of available engine parameters such as spark timing, compression ratio, displacement, and throttle actuation. A comparison of the efficiencies of the different types of engines showed an improvement of approximately 15% for the engine under partial load conditions and with variable displacement and compression ratio, compared to a conventional engine.

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The development of automotive propulsion has been guided in recent years by policies for the reduction of pollutant emissions. To comply with the imposed regulations, engine adaptability is one of the most effective strategies for meeting efficiency requirements in the case of the diverse operational conditions found in urban traffic. A variable stroke and compression ratio engine is the solution to this requirement. In addition to its advantages, its design inevitably increases the engine's complexity. Thus, it is necessary to conduct studies on the feasibility of such a technology. This work describes a variable stroke and compression ratio engine mechanism and presents a developed kinematic model that is used to evaluate the requirements for the implementation of this mechanism. The results of the evaluation confirm the possibility of using this alternative mechanism to obtain a higher efficiency in internal combustion engines.

By evaluating combustion duration and flame development, it is possible to evaluate the effects of utilizing a new type of fuel. This allows for optimization of the operational parameters such as the ignition timing, air–fuel ratio, and throttle opening with respect to efficiency, knock, emissions, and performance. In this work, the combustion of a Brazilian hydrous ethanol fuel was evaluated in a commercial flexfuel engine. Investigations were conducted by performing a heat release analysis of the experimental data and providing combustion characteristics. The experimental design comprised of variations in engine speed, load, ignition timing, and air–fuel ratio under lean condition. The results indicated the relationship between the engine parameters and combustion characteristics under a wide range of operational conditions, and identified the relationship between the physical characteristics of the fuels and their combustion in the commercial engine. For high engine speed, lean combustion presented a similar duration to the stoichiometric combustion duration. When comparing the combustion characteristics obtained for the hydrous ethanol with gasoline combustion, the main differences noted were reduced sensitivity to detonation and a shorter duration of combustion, although the temperature at the start of combustion was lower for ethanol. In addition to shorter combustion duration, ethanol presented a lower value for the Wiebe exponent. The results obtained from the combustion duration values and Wiebe function parameters enable the composition of a set of data required for a simplified combustion simulation.