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A number of studies in diesel dual fuel (DDF) operation which introduces natural gas from the intake pipe and ignites it by a diesel fuel injection in the combustion chamber have been conducted using conventional diesel engines. The present study investigated the influence of the ignition fuel on engine performance, combustion characteristics, and emissions with a combination of EGR and supercharging in DDF operation. The experiments employed iso-pentanol blended fuels for the ignition. Isopentanol is a next generation bio-alcohol fuel produced from cellulosic biomass, and actual use can be expected. The experiments were conducted at two CNG supply rates, 0% (ordinary diesel operation) and at a 40±4% (DDF operation) energy basis, and with EGR rates varied from 0 to 26%. The boost pressure was set at two conditions, 100 kPa (naturally aspirated, N/A) and 120 kPa (supercharged, S/C) with a supercharger.

The present study investigated the effect of boost pressure on the operation of a small single cylinder DI diesel engine equipped with a jerk type injection system fueled by different biodiesel fuels. The study employed a Roots blower type supercharger driven by a motor, and the boost pressures were varied from 100 kPa (naturally aspirated condition) to 140 kPa. The experiments used three kinds of biodiesel: rapeseed oil methyl ester (RME), soybean oil methyl ester (SME), and coconut oil methyl ester (CME). Further, a blended fuel with 60% (mass) CME and 40% 1-butanol (represented as CMEB) was also used. The influence of the boost pressure on the engine performance, combustion characteristics, and exhaust emissions with the abovementioned four biofuels were examined and compared with standard JIS No. 2 diesel fuel.

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.

This paper describes the influence of different kinds of FAME (fatty acid methyl ester) on the smoke emissions of a small single cylinder DI diesel engine and the soot formation characteristics in suspended single droplet combustion. The study used eight kinds of commercial FAME and diesel fuel blends. The tested FAMEs are saturated fatty acids with 8 to 18 carbon molecule chains, and with three different double bonds with C18. The results show that with all the FAME mixtures here, the brake thermal efficiencies with the FAME-diesel fuel blends were similar to neat diesel fuel operation while the smoke emissions with all of the tested FAME-diesel fuel blends were lower. To examine the differences in the soot formation characteristics, measurements of the formed soot mass were also performed with a basic experimental technique with suspended single droplet combustion. The soot was trapped on a glass fiber filter, and the mass of the filter was measured with an electronic microbalance.

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.

To utilize bio-butanol as an alternative diesel fuel, the effect of butanol isomer, where 1-butanol, 2-butanol and isobutanol were studied except for tert-butanol, on the combustion characteristics and exhaust emissions of butanol/gas oil blend was investigated using a DI diesel engine without modification of engine parameters. First, to understand the effect of butanol content on the diesel combustion, engine test was carried out using blends of 1-butanol which contents were 10 to 50 mass%. With increasing 1-butanol content, the Smoke emission reduces although the ignition delay gets longer and the HC and CO emissions increase especially at low load. The engine operation is stable except for full load with 1-butanol 50 mass% blend. From the above experimental results, butanol isomer blending ratio is set to 40 mass%.

This paper describes the fuel properties, combustion characteristics and exhaust emissions of the methyl esters of saturated fatty acid with 6 to 10 carbons in the molecule chain. The fuels blend (50/50 mass%) of three saturated fatty acid methyl esters (methyl caproate, methyl caprylate, methyl caprate); with methyl laurate as a base fuel are tested using a DI diesel engine. From the experimental results, the blend of saturated fatty acid methyl ester with a lower carbon number has a lower kinematic viscosity, pour point and smoke emission, though having longer ignition delay, the same as long chain saturated fatty acid methyl ester.

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.

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.

In order to improve the fuel properties and diesel combustion of biodiesel, waste vegetable oil methyl ester (from rapeseed and soybean oil mixture) with 5-20 mass% 1-butanol (BWME) are tested using a DI diesel engine. The viscosity and pour point of BWME decrease by blending 1-butanol. There is no problem in the startability and stability of the engine operation with BWME. Thermal efficiency of BWME is almost the same as that of the gas oil. The smoke emission decreases with increasing 1-butanol although the HC and CO emissions increase due to the longer ignition delay. It is concluded that BWME can be utilized as an alternative diesel fuel. Furthermore, to improve the ignitability and exhaust emissions of biodiesel with 1-butanol, palm oil methyl ester (PME) with high cetane number is tested as a base fuel of the 1-butanl blend. When the 1-butanol content in PME/1-butanol (BPME) is 15 mass%, BPME has almost the same ignition delay and HC and CO emissions compared with the gas oil.

In order to improve cold flow properties of palm oil biodiesel, varying the types of alcohol used at transesterification was examined. The pour point of palm oil biodiesel decreases as the carbon number of alcohol increases to 4. The pour point of palm oil isobutyl ester (PiBE) is lowest, 0°C, among 10 ester fuels made from different alcohols. The pour point of palm oil butyl ester (PBE) is 5°C, low for the second. Furthermore, PiBE, PBE, palm oil methyl, ethyl and propyl esters, rapeseed oil methyl ester (RME) and JIS No.2 diesel fuel (gas oil) were tested using a DI diesel engine. PBE and PiBE have the same thermal efficiency and NOx emissions compared to the other test fuels. HC, CO and Smoke emissions of palm oil ester fuels slightly increase when the carbon number increases. However, most of these exhaust emissions are lower than that of RME and the gas oil. From the experimental results, it is concluded that PBE and PiBE are good alternative diesel fuels.

In order to utilize tung oil as an alternative diesel fuel, the combustion characteristics and exhaust emissions of tung oil methyl ester (TME) were investigated by using a single cylinder DI diesel engine. Also the comparisons were carried out on combustion characteristics and exhaust emissions of TME with rapeseed oil methyl ester (RME) and JIS No.2 diesel fuel (gas oil). From the experimental results, the stable engine operation was achieved by fuelling TME as those of RME and the gas oil. The thermal efficiency of TME is almost the same as that of the gas oil. TME has longer ignition delay compared to the other test fuels due to the lower ignition ability. The pour point of TME is -7.5°C and that is the same as that of RME. The exhaust emissions (HC, CO, NOx and smoke) of TME are higher than those of RME and the gas oil. From the experimental results, it is necessary to improve the fuel properties of TME for better diesel combustion.

The fuel properties, the diesel combustion and the exhaust emissions of palm kernel oil methyl ester (PKME) and a blend of 20% PKME with 80% JIS No.2 gas oil (PK-B20) were investigated. In this study, the fuel properties were measured by laboratory analyses and the engine experiments were carried out by using a single cylinder direct injection diesel engine. To make comparison between biodiesels and conventional diesel fuel, palm oil methyl ester (PME), coconut oil methyl ester (CME), and the gas oil (JIS No.2) were also used as test fuels. From the fuel property analyses and the engine experimental results; the pour point of PKME was -5°C which was the same as that of CME and the pour point of PK-B20 was -10°C, the brake thermal efficiency of PKME was the same as the other test fuels, the ignition ability of PKME was better than that of the gas oil and the exhaust emissions (CO, HC, NOx and smoke) from PKME were almost the same as those of CME and lower than those of the gas oil.

In order to determine the usefulness of coconut and palm oil biodiesels as alternative diesel fuel, the fuel properties, the combustion characteristics and the exhaust emissions were investigated. Therefore, the methyl esters of coconut, palm and rapeseed oils (CME, PME and RME) and the ethyl ester of palm and rapeseed oils (PEE and REE) were processed and tested using a DI diesel engine. From the experimental results, the thermal efficiency of CME is almost the same as the other test fuels and CME has the lowest HC, CO, NOx and smoke emissions among the test fuels. Also PEE has the same ignitibility as PME and the exhaust emissions of PEE are almost the same as PME. From this investigation, we can say that CME and PEE are favorable alternative diesel fuels to substitute for petroleum based diesel fuel.

The diesel combustion characteristics and the exhaust emissions of biodiesel are affected by the composition of fatty acid methyl esters (FAMEs). In this study, the combustion characteristics and the exhaust emissions from single compositions of FAMEs, such as methyl palmitate, methyl oleate and the others, are investigated by using a single cylinder DI diesel engine. Experimental five FAME fuels are neat methyl oleate and the rest are blended mixtures based on methyl oleate. From the experimental results, the ignition delays of saturated FAMEs decrease with longer straight chain of the hydrocarbon molecules while in the same carbon number FAMEs, the ignition delays increase by increasing carbon-carbon double bonds. The break thermal efficiencies of the five FAME fuels and the gas oil are almost the same.

In order to reduce NOx and smoke emissions of palm oil methyl ester (PME), the combustion characteristics and exhaust emissions for emulsified PME were investigated using a single cylinder DI diesel engine. As the results, stable emulsified PME can be obtained without adding any emulsifier like as emulsified rapeseed oil methyl ester (RME). Emulsified PME is able to reduce NOx and smoke emissions as emulsified RME. The optimum water mass fraction for emulsified PME is 15wt% with regard to the exhaust emissions. The ignition delay of emulsified PME with 15wt% water is almost the same as that of gas oil because of the higher ignitionability of PME. Due to the higher ignitionability and better combustion characteristics of PME, emulsified PME with 15wt% water has shorter ignition delay and lower NOx, HC, CO and smoke emissions compared with emulsified RME with 15wt% water.