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Exhaust gases of diesel engines may be cleaned of particulates fairly effectively by filtering the gases through various types of beds. Filter regeneration is however, necessary to maintain a clean filter and to keep its flow resistance low. Uninterrupted regeneration may be achieved by burning up the trapped particulates in a continuous manner. Under high engine load conditions, this is attainable by reducing the ignition temperature of the particulates by means of suitable fuel additives, or by means of an appropriate catalytic coating of the relevant filter components. However, under low engine loads, the exhaust gas temperature might be too low and another sensible method has to be employed to continuously ignite the particulates. Apparently, the minimum required exhaust temperature may be achieved over a fairly wide range of engine operation conditions by using several simple-to-employ means.

The effect of oxygen-containing additives on the toxic emission of a SI engine, has been studied. The relationship between the chemical structure of the additives, their oxygen content and molecular mass, and the chemical composition of the exhaust gas toxic compounds (CO, HC and NOx), has been established. More than 20 samples of fuel blends containing oxygenates, were tested. The tested oxygenates represent three large chemical structure categories which can be found in the chemical industry wastes - alcohols, ethers and ketones. The tests were performed using a four-cylinder, spark-ignition engine. In order to determine the optimum types of fuel additives for the suppression of carbon monoxide, hydrocarbons and nitro-oxygens, fuel blends containing 10% oxygenates with different oxygen content (from 9% to 50%) and molecular mass (from 32 to 170) were examined.