Abstract
Abstract
This study focuses on the conversion of a turbocharged compression-ignition (diesel) engine UR-II 8602.12, originally installed in the Zetor 16145 tractor, into a spark-ignition (gas) unit operating on gaseous fuel. The study presents experimental results of performance, fuel economy, and emission characteristics under full-load speed sweep as well as part-load operation. The converted engine achieved a maximum corrected power output of 106.5 kW at 2200 rpm, representing an 8.5% reduction relative to the original diesel engine (116.5 kW). The corrected peak torque reached 462 N·m, which is 21% lower than the baseline diesel torque of 583 N·m. From an environmental perspective, carbon monoxide emissions remained very low (~0.05 vol. %), while hydrocarbon concentrations decreased with increasing mixture enrichment (from 377 ppm to 245 ppm). However, nitrogen oxides (NO
x
) exceeded the threshold of 500 ppm across the entire speed range, peaking at 2282 ppm at the maximum speed. Exhaust gas temperatures behind the turbine reached up to 650 °C, which, after accounting for thermal gradient, implies that the recommended limit of 630 °C at exhaust valves is exceeded at higher loads. The findings demonstrate that natural gas conversion can retain favourable power characteristics while lowering carbon-based emissions, yet further optimisation is required to control thermal stress and mitigate NO
x
formation.