Diesel Engine Performance and Combustion Imaging Analysis of Gas-to-Liquid and Polyoxymethylene Dimethyl Ether Blended Fuels

To reduce carbon dioxide emissions from automobiles, the introduction of electric vehicles to the market is important; however, it is challenging to replace all existing IC engine vehicles with electric ones. Consequently, there is increasing anticipation for the use of carbon-neutral fuels, such as e-fuels.

This study investigates the effects of GTL (gas-to-liquid), as a substitute for e-fuel, produced from natural gas via the Fischer–Tropsch synthesis method and polyoxymethylene dimethyl ether (OME_mix) produced from methanol, on engine performance. Additionally, combustion image analysis was conducted using a rapid compression and expansion machine (RCEM).

GTL fuel combusts similarly to conventional diesel fuel but has slightly lower smoke emissions because it does not contain aromatic hydrocarbons. Further, its high cetane number results in better ignition properties. During the combustion, unburnt hydrocarbons and smoke are generated in the spray flame interference region near the cylinder wall due to insufficient oxygen, and as it moves from the cylinder wall toward the center of the cylinder, the re-oxidation is observed, which is reflected in the heat release rate as the after-burning duration.

When the OME_mix is mixed with hydrocarbon fuels such as GTL, combustion continues even in the spray flame interference region, leading to a reduction in the after-burning duration and significantly lower smoke emissions.

Further, the GTL was divided into four distillation regions, that are GTL Light, GTL Light Middle, GTL Middle Heavy, and GTL Heavy, and the effects of low and high-boiling fractions in GTL on diesel combustion were investigated. Heavy fractions have excellent ignition properties, resulting in shorter lift-off (set-off) length during combustion. However, due to the poor evaporation characteristics, they have longer high-temperature residence time, leading to greater cooling losses and reduced thermal efficiency. On the other hand, light fractions have longer lift-off lengths, mix well with air before combustion, and have shorter combustion durations compared to heavy fractions. Finally, an engine performance was evaluated using a fuel mixture of the fuel with the heavy fractions removed from GTL (heavy-cut GTL) and OME_mix in a 1:1 ratio.