Experimental assessment of waste cooking oil biodiesel–butanol–diesel ternary blends in a CRDI engine: combustion dynamics, performance optimisation, and emission profiling.

The focus of this study is the effects of combustion dynamics, performance optimisation, and emissions profile on compression-ignition (diesel) engines operating on ternary fuel formulations comprising waste cooking oil (WCO), butanol, and conventional petroleum-based (diesel) fuel. The primary physicochemical characteristics of these WCO-butanol-diesel fuel formulations were almost identical to those observed with conventional petroleum-based diesel fuel, thereby conforming to both ASTM D6751 and EN 14214 specifications; these include density, kinematic viscosity, and flash point. The variation of the butanol concentration from 10% to 30%, as well as the volume fractional distribution of the WCO from 10% to 40% vol., resulted in significant differences in the thermodynamic response of the engine test rig used for this lab evaluation. Additionally, the D60B20Bu20 ternary blend produced a 7.14% increase in brake thermal efficiency (BTE), from pure (D100) diesel fuel to the D60B20Bu20 baseline; there was also a corresponding reduction in brake-specific fuel consumption (BSFC) by 6.84% and brake-specific energy consumption (BSEC) by 6.00%. The exhaust gas temperature (EGT) for the alcohol-treated ternary coatings was significantly lower than that of pure diesel due to the high latent heat of vaporisation of butanol. The application of advanced environmental profiles on these results demonstrated significant reductions in emissions of regulated pollutants. The most pronounced results were seen with the use of the D60B20Bu20 formulation, which resulted in the largest reduction in both carbon monoxide (CO) emissions (15.94%), and unburned hydrocarbons (HC) (22.85%), respectively; there was also a significant reduction in smoke opacity at high load operating conditions. In contrast to the above, there was an average overall improvement of 7.74% in thermal nitrogen oxide (NOx) emissions across all blends due to both the very high premixed heating phase and the availability of fuel-bound oxygen. Additionally, transient combustion data demonstrated that the D60B20Bu20 matrix achieved the highest peak in-cylinder pressure, maximum mean gas temperature and greatest sharpness of net heat release rate (HRR). This study provides preliminary evidence that a multi-criteria optimisation framework can be used to identify the best overall compromise between aggressively reducing carbonaceous emissions while achieving improved thermodynamic performance with the D60B20Bu20 blend.