Statistical modelling and multi-response optimization using RSM of a hydrogen-enriched low duty CRDI engine with NH3-based urea selective catalytic reduction at higher fuel injection pressures: An experimental analysis

Abstract

This study investigates the performance and emission characteristics of a single-cylinder, water-cooled, four-stroke CRDI diesel engine using three fuel configurations: pure diesel, dual-fuel (diesel + hydrogen), and dual-fuel with NH₃-based urea injection into the exhaust system, a novel approach that integrates hydrogen enrichment with SCR-based emission after-treatment, along with statistical analysis and validation using Response Surface Methodology (RSM). The tests were conducted at constant engine speed (1500 rpm), injection timing (23° bTDC), and compression ratio (18), across varying loads (12.5–50 Nm) and fuel injection pressures (600, 750, and 900 bar). Hydrogen's superior flame speed and thermal properties improved combustion efficiency, while urea injection provided selective non-catalytic reduction of NOx emissions. RSM was employed for multi-objective optimization and statistical validation of engine behaviour. Under dual-fuel operation with urea at full load and 900 bar FIP, the engine achieved a maximum BTE of 49.63 %, and a minimum BSFC of 0.10 kg/kWh. Although volumetric efficiency slightly declined in dual-fuel mode due to hydrogen's low density, it was partially improved with urea injection, peaking at 83.72 % at 12.5 N m and 900 bar. Emission results showed a 17.45 % reduction in NOx (from 1490 to 1230 ppm), 18.60 % reduction in HC (from 41 to 34 ppm), and 11.94 % reduction in CO₂ (from 3.05 % to 2.68 % by vol) with urea-injected dual-fuel mode. Mathematical analysis of the experiment is conducted using RSM, and optimization is carried out of the said model using desirability. The optimal operating point of 846.84 bar FIP and 23.54 Nm load achieved a BTE of 37.02 %, BSFC of 0.256 kg/kWh, and a high desirability index of 0.841. Overall, hydrogen dual-fuel operation with NH₃-based urea injection effectively enhances engine performance and reduces emissions. The findings provide a promising framework for developing cleaner and more sustainable combustion systems that address the dual challenge of performance optimization and emission control.