Evaluation of Synthetic Gasoline Fuels and Alcohol Blends in a Spark-Ignition Engine

Renewable synthetic fuels offer the opportunity to significantly reduce carbon dioxide (CO₂) emissions worldwide if burned in the internal combustion engines of existing and future passenger car fleets. To evaluate this potential, two renewable synthetic gasoline fuels and alcohol blends that can be produced via the methanol-to-gasoline (MtG) synthesis process are evaluated in this study. The first synthetic gasoline, hereafter referred to as MtG, was developed by Chemieanlagenbau Chemnitz GmbH and Technische Universität Bergakademie Freiberg, produced within the closed carbon cycle mobility (C³-Mobility) project, and was blended with 10%(V/V) ethanol (MtG-E10), 20%(V/V) ethanol (MtG-E20), 15%(V/V) methanol (MtG-M15), and 15%(V/V) 2-butanol (MtG-2Bu15). The second synthetic fuel, named POSYN (POrsche SYNthetic fuel), was developed by Porsche. The suitability of the synthetic fuels was experimentally investigated in a spark-ignition (SI) single-cylinder research engine with a compression ratio (CR) of 10.8 and compared with conventional gasoline fuel with Research Octane Number 95 and 10%(V/V) ethanol (RON95 E10) gasoline fuel. Load variations at a constant engine speed of 2500 rpm showed no significant differences between Methanol-to-Gasoline with 10%(V/V) ethanol (MtG-E10) and RON95 E10 in terms of both combustion performance and emissions. Additionally, a load variation with MtG-E10 and RON95 E10 at an engine speed of 3000 rpm was performed on a commercially available BMW multi-cylinder engine (MCE), which confirmed that both these fuels show an almost identical combustion and emission behavior. However, the knock resistance improved with higher alcohol fractions. Because of the favorable anti-knock properties of methanol, Methanol-to-Gasoline with 15%(V/V) methanol (MtG-M15) showed the highest maximum net indicated efficiency of 39.33%. This is 2% more than with Methanol-to-Gasoline with 20%(V/V) ethanol (MtG-E20), despite the lower alcohol volume fraction. In contrast, Methanol-to-Gasoline with 15%(V/V) 2-butanol (MtG-2Bu15) showed no improvement. POSYN enabled a significant efficiency advantage over RON95 E10 because of its high knock resistance, however, achieved the same maximum engine load because of the reduced octane sensitivity. The variation of the relative air/fuel ratio at an engine speed of 2500 rpm and an engine load of 16 bar net indicated mean effective pressure confirmed these findings. The highest net indicated efficiency of 42.4% was achieved with POSYN at a relative air/fuel ratio of 1.6. The lean limit could not be increased with the synthetic fuels and alcohol blends albeit with an improved combustion stability.