Multiple injection strategies in diesel engines are known to reduce pollutant emissions directly in the combustion chamber, while biodiesel made from waste cooking oil (WCO) has been studied mainly using single injection. In the current study, they were combined to evaluate biodiesel's potential based on a parametric study of the injection strategy. The main findings are that pilot injection increased the sensitivity of early main-injection timing by decreasing the main-injection ignition delay. Furthermore, for some injection strategies, the pressure wave in the injector's feed pipe also impacted the resulting pollutant emissions. Thus, the optimum double-injection strategy, allowing decreased PM and NOx emissions, was obtained with a slightly retarded main-injection timing in comparison to the optimum single-injection strategy. Waste-cooking-oil biodiesel blended with diesel (20% to 80% proportion) has, however, shown higher PM emissions and lower NOx emissions compared to diesel when a single-injection or an optimal double-injection strategy is used.