Effect of fuel injection timings on performance and emissions of stratified combustion CNGDI engine

•Compressed natural-gas direct injection engine with stratified combustion is tested.•The highest power, torque, mean effective pressure and lowest brake specific fuel consumption is at EOI 120 BTDC.•Lambda is shown a lean mixture at all combustion conditions that decreased fuels' consumption.•Carbon dioxide (CO2) emission was high at 120 BTDC on the high engine speeds.•The lowest (NO) and (HC) were founded at 120 BTDC.

This study investigates the effect of various injection timings on the performance and emissions of stratified combustion compressed natural-gas direct injection. The engine of 1.6 l, spark ignition, four cylinders fuelled with compressed natural gas was tested. The engine test bed using Kronos software and the exhaust emission were recorded using portable exhaust gas analyser Kane-May. All tests were occurred under wide throttle open with various injection timings (EOI 120, EOI 180, EOI 300, EOI 360) BTDC. Results show high power, torque and brake mean effective pressure (BMEP) at 120 BTDC. The lowest brake specific fuel consumption (BSFC) is at 120 BTDC. Lambda is shown higher than one, which is mean lean mixture air-fuel. Carbon monoxide (CO) emission is low at 360 BTDC at low speeds but at high speed, it was low at 120 BTDC. Carbon dioxide (CO2) emission was high at 120 BTDC on the high engine speeds. The lowest (NO) and (HC) were founded at 120 BTDC. However, the combustion pressure and the PV were recorded for all injection timings under various engine speeds.