An experimental study of using coal to liquid (CTL) and diesel as pilot fuels for gasoline dual-fuel combustion

•The coal to liquid (CTL) was applied as pilot fuel on the dual-fuel engine.•The dual-fuel combustion mode can significantly improve the ITE.•Compared with diesel, using CTL as pilot fuel improves the ITE and reduces PPRR.•The gasoline/CTL dual-fuel mode can improve the ITE and pollutant emissions.