Amid the prevalence of some plant based biofuels, we have targeted on optimizing the use of a new biofuel, pine oil, in a diesel engine without resorting to any engine modifications. Pine oil, extracted from the resins of pine tree, has some remarkable fuel properties such as lower viscosity, flash point and boiling point than diesel, while its calorific value is comparable to diesel. However, the cetane number of pine oil is lower and hence when being used as blends with diesel, it exhibits prolonged ignition delay and higher peak heat release rate, paving way for more NOX emission. Compared to fossil diesel, experimental investigation of 50D: 50B (50% diesel and 50% pine oil) in a diesel engine showed significant decrease in CO (carbon monoxide), HC (hydrocarbon) and smoke emission by 45.9%, 32.4% and 41.5%, respectively, whereas the NOX (nitrogen oxides) emission was noted to be increased. To help reduce the negative impact of pine oil on NOX emission and ignition delay, this work intends to add two ignition promoters, IAN (iso-amyl nitrate) and DTBP (di-tertiary butyl peroxide), with 50D: 50B. After the addition of ignition promoters, the NOX emission for 50D: 50B-IAN and 50D: 50B-DTBP is decreased by 12.8% and 19.2%, respectively, compared to 50D: 50B. Among the two ignition promoters, DTBP is more effective in reducing NOX emission, adding to the other benefits of reduced CO and HC emission by 40% and 34%, respectively, than 50D: 50B. In addition, the performance of the engine was also noted to be improved for 50D: 50B-DTBP, suggesting that DTBP is a pertinent ignition improver for pine oil-diesel blends. (C) 2013 Elsevier Ltd. All rights reserved.