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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 natural gas 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 gas oil. 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 clarify the influence of the cetane number (C.N.) of the ignition fuel on the ignition performance, combustion characteristics, and emissions of the dual fuel operation, the present study used standard ignition fuels prepared by n-hexadecane and heptamethylnonane which define the ignitability of diesel combustion.

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 reduce the smoke emission of PME/1-butanol blend by increasing the 1-butanol content, PME/1-butanol blend is tested using a DI diesel engine with jerk-type fuel injection pump. With PME/1-butanol blend, there is no problem on the start-ability and stability of the engine operation up to 60 mass% of 1-butanol. On the other hand, with gas oil/1-butanol blend, there is no problem on those up to 40 mass% of 1-butanol. The PME/1-butanol blend has longer ignition delay compared with PME due to the low cetane number of 1-butanol. With increasing 1-butanol content, the smoke emissions of PME/1-butanol blend decrease although the HC and CO emissions increase due to the longer ignition delay.

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.