systematic study was conducted to make a comparative evaluation of the effects of blending n-butane and n-pentagonal with bio diesel at 10% and 20% by volume on engine performance and on the physic chemical characteristics of particulate emissions from a single cylinder, direct injection diesel engine.The engine was operated at a constant engine speed and at three engine loads. Compared to bio diesel, butane–bio diesel blends lead to a maximum of 1.6% increase in the brake thermal efficiency (BTE) and an increase in the brake specific fuel consumption (BSFC) by 1.9–3.9% at low and medium engine loads. Pentagonal–bio diesel blends result in an improvement in the BTE and a maximum of 2% increase in the BSFC. Compared to bio diesel, both the blended fuels can reduce the particulate mass and elemental carbon (EC) emissions, with butane being more effective than pentagonal. The blended fuels also show a lower emission of total particle-phase poly cyclic aromatic hydrocarbons (PAHs) and also a lower carcinogenic potential. However, the proportion of particulate-bound organic carbon (OC) and water-soluble organic carbon (WSOC) are increased for the both blended fuels, especially for 20% butane in blends.The emissions of volatile and solid particles are reduced significantly in terms of their counts for both kinds of blended fuels at medium and high engine loads, whereas the total particle counts for both 10% and 20% butane in blended fuels are increased at low engine load due to a significant increase in particles with diameter less than 15 mm.