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Experimental aviation engines face numerous challenges, including the need for energy efficiency, alternative fuel sources, reduced weight and size, greater durability with reliability, emissions reduction, and integration with advanced control and monitoring systems. This study presents the performance of a two-stroke engine with a Uniflow scavenging system with a flathead valve concept, with lower specific fuel consumption than conventional two-stroke aircraft engines. The engine’s maximum speed is limited to 3000 rpm for better cylinder scavenging efficiency, which also eliminates the need for a reduction gearbox, simplifies the design, and reduces the engine’s total mass. 1D simulations were conducted to evaluate combustion and performance parameters using aviation.

Homogeneous charge compression ignition (HCCI) combustion is low-temperature combustion (LTC) mode that offers an alternative to conventional combustion modes. The advantages of HCCI combustion include high conversion efficiency and low NOx emissions. On the other hand, a direct control mechanism for combustion phasing control is not attainable as in conventional SI (spark ignition) or CI (compression ignition) engines. This limits the HCCI operational range and provides one of the biggest challenges in HCCI mode commercial implementation. High heat release rates and knock initiation limit the high load operation, whereas combustion instabilities limit the low load operation. In this context, this paper explores the use of water injection technique to control the combustion phasing and expand the load of an ethanol HCCI engine.

Stringent emission legislations have pushed engine operation to borderline knock. Knocking combustion limits engine efficiency, putting a threshold in carbon emission reduction that impairs further decarbonization of the transport sector. In this way, online knock monitoring is very important during engine development and calibration to allow operation with higher efficiency levels. Commonly, knock detection methods require complex calculations with high computational cost. Furthermore, these methods normally need previous calibration of a threshold value for each specific engine to indicate the knock limit, requiring important engineering resources and time. Hence, this paper proposes a novel methodology for knock detection that is simple, does not require prior calibration and can be used for sensorless knock detection. The method is applied by relating the crank angle of maximum pressure rise rate (AMPRR) with the angle of 50% of fuel mass burned (CA50), the so-called G Index (GI).

Ethanol with high levels of hydration is a low cost fuel that offers the potential to replace fossil fuels and contribute to lower carbon dioxide (CO2) emissions. However, it presents several ignition challenges depending on the hydration level and ambient temperature. Advanced combustion concepts such as homogeneous charge compression ignition (HCCI) have shown to be very tolerant to the water content in the fuel due to their non-flame propagating nature. Moreover, HCCI tends to increase engine efficiency while reducing oxides of nitrogen (NOx) emissions. In this sense, the present research demonstrates the operation of a 3-cylinder power generator engine in which two cylinders operate on conventional diesel combustion (CDC) and provide recycled exhaust gas (EGR) for the last cylinder running on wet ethanol HCCI combustion. At low engine loads the cylinders operating on CDC provide high oxygen content EGR for the dedicated HCCI cylinder.

This study evaluates the performance of an ethanol fueled spark ignited engine running with high levels of hydration. Ethanol is a renewable fuel and has been considered a promising alternative to counteract global warming and to reduce pollutant emissions. Its use is well established in ICE as the main fuel or blended with gasoline. However, due to its lower calorific value, it shows increased fuel consumption when compared to gasoline, rendering its use sometimes less attractive. The energy demand to produce ethanol, especially at the distillation phase, increases exponentially as the concentration of ethanol-in-water goes from 80% onwards. Thus, mixtures with less than 80% of ethanol-in-water would reduce the energy consumption during production, yielding a less expensive fuel. In previous studies, to evaluate the feasibility of wet ethanol as a fuel for spark-ignited engines, results have shown that it was possible to use mixtures of up to 40% of water-in-ethanol.