In this study, we investigate the dual-fuel operation of compression ignition engines using biodiesel at varying concentrations in combination with biogas, with and without hydrogen enrichment. A response surface methodology, based on a central composite experimental design was employed to optimize energy efficiency and minimize pollutant emissions. The partial substitution of diesel with gaseous fuel substantially reduces the specific fuel consumption, achieving a maximum decrease of 21% compared with conventional diesel operation. Enriching biogas with hydrogen, accounting for 13.3% of the total flow rate, increases the thermal efficiency by 0.8%, compensating for the low calorific value and reduced volumetric efficiency of biogas. Variations in biodiesel concentration exhibits a nonlinear effect, yielding an additional average efficiency gain of 0.4%. Regarding emissions, the addition of hydrogen to biogas contributes to an average reduction of 5% in carbon monoxide emissions compared to the standard dual-fuel operation. However, dual-fuel operation leads to higher unburned hydrocarbon emissions relative to neat diesel; hydrogen enrichment mitigates this drawback by reducing hydrocarbon emissions by 4.1%. Although NO_x emissions increase by an average of 26.6% with hydrogen addition, dual-fuel strategies achieve NO_x reductions of 11.5% (hydrogen-enriched mode) and 33.3% (pure biogas mode) relative to diesel-only operation. Furthermore, the application of response surface methodology is robust and reliable, with experimental validation showing errors of 0.55–8.66% and an overall uncertainty of 4.84%.

The combination of crambe (Crambe abyssinica L.) biodiesel and diesel S10 could be a fuel-renewable alternative for internal combustion engines. However, little is known about the comparison of fuels and different blends. Therefore, the study's objective was to evaluate the effects of crambe biodiesel and diesel S10 blends on the emission and engine performance of a diesel engine. Four biodiesel blends were used (B10, B15, B20, and B100) and operated with an electrical power range of 0.5 kW until 2.5 kW at 3000 rpm. The D100 blend consisted of pure diesel S10. The parameters measured were specific fuel consumption (SFC), exhaust gas temperatures (EGT), smoke emission, particulate matter (PPM), oxides of nitrogen (NOx), monoxide carbon (CO), hydrocarbons (HC) and carbon dioxide (CO2). The lowest NOx, HC, CO2, and SFC, were observed for the B20 crambe blend at full load conditions when compared to other blends. The crambe B20 reduced the specific consumption by 16,5% in relation to diesel at a load of 100%. Therefore, the crambe B20 can be an interesting blend for engine use.