Impacts of methanol blended fuels on emissions and operating performance of two-wheelers

Aiming to investigate the influence of methanol blends on the combustion process of a PFI four-stroke boxer engine, four mixtures of pure methanol and oxygen-free gasoline (M0) are prepared. The fuels tested are labelled by M15, M25, M35 and M50, where the number represents the percentual in volume of methanol within the mixture. In order to establish a base for comparisons, standard gas-station gasoline (S95) is also tested. Backwards compatibility is evaluated through test-bed measurements, when the engine operates without any modifications in the ECU. Over the whole operational area of the engine map, M15 and M25 can be used in the motorcycle application. Raw emissions of THC, CO2, CO and NOx decrease with the increase of methanol for almost all the conditions tested. It is observed that knock resistance is higher for higher methanol contents. At WOT, power is increased with the methanol proportion, being M50 and M35 more powerful than standard gasoline. Indicated efficiency also increases with methanol percentage, all the mixtures show a higher efficiency than standard gasoline. The most common WMTC load points are studied in order to evaluate the after-catalyst emissions. Compared to gasoline and oxygen-free gasoline, a significant reduction of NOx is observed. As the combustion temperature of M15 and M25 drops and no optimization of the exhaust aftertreatment was performed, this results in an excess of THC and CO when compared to gasoline.