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Transesterified fuels (biodiesel fuels; BDF) from vegetable oils are alternative fuels for diesel engines, they are renewable and offer potential reductions in carbon dioxide emissions. Many studies have reported that exhaust from BDF has equal or higher NOx concentrations while HC and PM emissions are significantly lower than with gas oil. The aim of the present investigation is to achieve drastic reductions in NOx emissions. Performance tests of a single cylinder DI diesel engine were conducted using water emulsified fuels from BDF and gas oil with varying water addition rates combined with cooled EGR. The result showed that at a rated output, the emulsified gas oil with water to base fuel volume ratio of 30% reduced NOx (from 1020ppm) to 190ppm with the 21% EGR condition maintaining the minimum BSEC value achieved with EGR free gas oil operation. However, the smoke density increased by 28%.

Dual fuel diesel engines using compressed natural gas (CNG) are an attractive low polluting application, because natural gas is a clean low CO2 emitting fuel with superior resource availability. In dual fuel diesel engines with CNG as the main fuel the natural gas is supplied from the intake-pipe and the pre-mixture formed in the cylinder is spontaneously ignited by an injected spray of ordinary diesel fuel. Dual fuel engines of this type have the advantages that only limited engine modifications are needed and that low calorie gas fuels such as biogas can be used. To reduce NOx emissions in the dual fuel operation, the present study conducted the diesel combustion with a setup similar to that used with EGR. To dilute the intake air, the experiments used N2 or CO2 gases which are the major components of EGR. The diluent gas addition ratio was defined as the mass ratio of the supplied diluent to the intake charge which is composed of air and diluent.

In order to improve the cold flow properties of coconut oil biodiesel and to reduce the lifecycle CO2 emission by using bio-alcohol at biodiesel manufacturing, varying the types of alcohol used at transesterification was examined. The pour point of coconut oil ester decreases as the carbon number of alcohol increases. Among 5 ester fuels, the pour point of coconut oil isobutyl ester (CiBE) made from isobutanol is lowest, −12.5 °C, compared to that of coconut oil methyl ester (CME), highest, −5 °C. The pour point of coconut oil 1-butyl ester (CBE) is −10 °C, second lowest. Furthermore, CBE, CiBE, CME and JIS No.2 diesel fuel (gas oil) were tested using a DI diesel engine. CBE and CiBE have shorter ignition delay compared to the gas oil although slightly longer than CME. CBE and CiBE have the same thermal efficiency and NOx emissions compared to the gas oil. HC, CO and Smoke emissions of coconut oil ester fuels slightly increase when the ester molecule carbon number increases.