In previous research, there have been more investigations on methanol blended with other fuels such as diesel, biodiesel, gasoline, etc., but fewer investigations on methanol with ignition additives as a mono-fuel. To better understand the methanol mono-fuel combustion characteristics and to further apply them, a combined experimental and simulation study of methanol in a Scania heavy-duty compression ignition (CI) engine was carried out in this work. The experiments consisted of four groups with variable injection timings, variable fraction of ignition additives, variable charge air temperatures, and variable overall excess air ratios/power sweeps. Heat release rate (HRR), cylinder pressure, ignition delay and indicated efficiency were analyzed for each case. The analysis showed that the combustion type was partially premixed combustion (PPC) in some cases and diesel-like combustion in the rest. By observing all cases, the shortest ignition delay was 14.1°, and the longest was 22.8°. The indicated efficiencies were in the range of 0.35 to 0.43. Simulations and validation analyses were performed for all cases by a multi-packets model. The physical and chemical ignition delays were predicted. The physical ignition delays were in the range of 4.25 to 8.10°, and the chemical ignition delays were in the range of 6.66 to 17.1°. The chemical ignition delay was always longer than the physical one. This indicates that chemical ignition delay has to be prioritized to improve the ignition performance of methanol fuel.
Methanol, as one of the significant green fuel candidates for the combustion engines, can be produced from Power to X and biomass production. However, compression ignition (CI) of pure methanol in a combustion engine is impractical due to its low cetane rating. The strategy has gained little attention in the past, but is possible if the methanol is premixed with a fuel additive (ignition improver). In order to optimize and understand additivated methanol combustion, a phenomenological spray/packet combustion model is developed in this work. The model is used to calibrate an Arrhenius-type ignition delay equation for CI engine using additivated methanol, and the resulting calibrated ignition delay parameter is 2.14. The procedure involves to compare the modeled and experimental combustion rate profiles that are derived from a small marine CI engine by burning methanol with 3.5 % and up to 7.5 % kg/kg fuel additive. The present work finds that the phenomenological diesel combustion model methodology can be used with good accuracy, to simulate combustion rate profiles of additivated methanol in a CI engine. The model is, furthermore, able to indicate intermediate variables such as burning packet speeds, air mass, droplet mass, air/fuel equivalence ratio, and burning packet temperature for different packets of combustion.