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The boiling point curve of fatty acid methyl esters (FAME), or biodiesel fuel, can be adapted to that of diesel fuel by breaking FAME down into a low-molecular structure using a cross-metathesis reaction with a short-chain olefin. Reformulated FAME by a metathesis reaction consists mainly of medium-chain olefins and fatty acid methyl esters. In the present study, the engine performance and exhaust emissions from reformulated FAME were investigated through engine bench tests. Surrogate fuels made from typical chemical components of reformulated FAME were used to clarify the effects of respective components upon combustion. Surrogate fuels were made by mixing 1-decene, 1-tetradecene, methyl laurate, methyl palmitate, and methyl oleate to simulate the boiling point, oxygen mass concentration, and calorific value of reformed biodiesel of waste cooking oil methyl ester (WME). A single-cylinder diesel engine equipped with common-rail-type injection system was used.

Biodiesel fuel (Fatty acid methyl esters: FAME) have lower volatility than petro-diesel fuel due to the larger molecular size of FAME. Recent studies report that the distillation temperature of biodiesel fuel can be lowered by the cross-metathesis reaction with short-chain olefin using ruthenium catalyst. In this study, the effect of cross-metathesis reaction conditions on the distillation characteristics of reformulated biodiesel fuel is investigated to reveal the reaction conditions for fitting the distillation curve of biodiesel fuels to that of petro-diesel fuel. Furthermore, the reactivity of typical biodiesel fuels such as RME (rapeseed oil), SME (soybean oil), and WME (waste cooking oil) for cross-metathesis reaction were examined to reveal the reaction conditions appropriate for their fatty-acid compositions.

“Drop-in” biofuels have a high potential as an alternative to petro-fuels. Because drop-in biofuels are hydrocarbon fuel, there are no issues related to poor oxidation stability such as in FAME. Diesel fuel which is named “SoladieselRD” is liquid bio-hydrocarbon and is the hydro-treated oil of micro-algal triglyceride. In this study, the engine performance and exhaust emission characteristics using SoladieselRD were investigated and compared with those using petro-diesel fuel (gas oil). A test was conducted using a single-cylinder, water-cooled, direct-injection diesel engine with a common-rail type high-pressure injection system. From the experimental results, it was clear that the ignition delay of SoladieselRD is shorter than that of petro-diesel, and the trade-off relationship between PM and NOx emissions by SoladieselRD was better than that of gas oil.

The main aim of this study is to investigate the effect of NO and NO2 on the combustion characteristics such as pressure development and combustion phasing in natural gas HCCI engine. A secondary aim is to demonstrate a method of obtaining a significant sensitizing effect on methane oxidation reaction from small amounts of NOx. Experiments were conducted using a rapid compression-expansion machine that was constructed from a single-cylinder diesel engine. First, the sensitizing effect of NO and NO2 on the HCCI combustion of natural gas was investigated in a case where NOx was uniformly mixed into a charge. Obtained results show that the auto-ignition timing is significantly advanced and an acute heat release is promoted by adding either NO or NO2.

The objective of this study was to obtain an improved understanding of the effects of the simultaneous use of cold flow improver (CFI) and antioxidant on the cold flow properties, oxidation stability and diesel exhaust emissions of various biodiesels and biodiesel blends. Cold flow properties were evaluated by assessing the cloud point (CP) and pour point (PP) values, as well as from the results of the cold soak filtration test (CSFT). Oxidation stability was also determined by measuring the peroxide induction period (IP). The neat biodiesels (B100) derived from soybean oil(SME), Jatropha curcus oil(JME), rice bran oil(RBME), palm oil(PME) and waste cooking oil(WME), and biodiesel blends with JIS No.2 diesel fuel were tested. A CFI and antioxidant specially designed for use in biodiesel fuels were employed during the work. The experimental data demonstrated that the addition of antioxidant had no effect on either the CP or PP values.

High energy demand and environmental pollution leads to seeking of new, renewable and clean energy as biofuel and biomass. These fuels are abundant in tropical areas and agricultural-economic-based countries. Among various crops which are used for biofuel, Jatropha Curcas L. Oil (JO) is more beneficial and attractive as it is non-edible which is not competitive with food demand. In agricultural sector, the biomass waste especially from rice production such as rice husk is a tremendous resource in Cambodia. The combination of the use of biomass from rice husk (RH) and Jatropha Cake (JC) from the JO production in the gasification can produce more energy for the electricity production especially in the remote and rural area. In previous research, some researchers have been investigated on the use of JO in blending ratio, heated-neat condition and dual fuel combustion of diesel and bio-digested biogas.

The suitability of caprylic (C8:0), lauric (C12:0), and palmitic (C16:0) acid 2-ethylhexyls derived from palm/coconut oil in diesel engine was evaluated. The pour point of each compound was approximately 40°C lower than that of the corresponding methyl ester due to the ethyl branch in the alcohol. All compounds possessed high oxidation stability, high lubricity, and a high cetane number. Engine bench test results demonstrated that 2-ethylhexyl laurate and palmitate result in shorter ignition delays compared to gas oil. The short ignition delays suppressed initial premix-like combustion. As a result, high brake thermal efficiency with low combustion noise was achieved. Furthermore, both laurate and palmitate produced less NOx emissions and less unburned gaseous emissions.

This study focuses on deposit formation in a diesel engine fueled with straight vegetable oil (SVO) and its effects on engine performance and exhaust emissions. First, two-dimensional thickness distributions of the carbon deposits on the cylinder head were measured by a laser displacement meter after continuous engine operation on gas oil blended with SVO at 25%. The obtained results show that the carbon deposit thickness rapidly increases with SVO-blended fuel and reaches a higher level than with just gas oil. Second, the effects of fuel injector deposits on engine performance and emissions were examined. A small diesel engine was continuously operated by alternating between SVO and gas oil. Gas oil was injected for 1 hour before and after 6 hours of SVO operation to prevent the accumulation of SVO deposits inside the nozzle holes, and the process was repeated.

To control natural-gas HCCI combustion, internal exhaust gas recirculation (EGR) by exhaust valve reopening (EVRO) during the induction stroke was applied to a single-cylinder test engine. The results demonstrate that combustion phasing can be controlled successfully by adjusting the EGR ratio, and so improvement of thermal efficiency and reduction in unburned exhaust emissions are feasible. In addition, the results of the EVRO method were compared to those of intake-valve pilot opening (IVPO) during the exhaust stroke. It was shown that EVRO is more useful than IVPO as a heat-recovery method for HCCI combustion.

In a DI diesel engine, THC emissions increase significantly with lower compression ratios, a low coolant temperature, or during the transient state. During the transient after a load increase, THC emissions are increased significantly to very high concentrations from just after the start of the load increase until around the 10th cycle, then rapidly decreased until the 20th cycle, before gradually decreasing to a steady state value after 1000 cycles. In the fully-warmed steady state operation with a compression ratio of 16 and diesel fuel, THC is reasonably low, but THC increases with lower coolant temperatures or during the transient period just after increasing the load. This THC increase is due to the formation of over-lean mixture with the longer ignition delay and also due to the fuel adhering to the combustion chamber walls. A low distillation temperature fuel such as normal heptane can eliminate the THC increase.

In this study, it was attempted to operate the 4-cycle multi cylinder natural gas engine introduced PCCI combustion system without electric heater for intake air heating. In experiment, by optimization of the compression ratio and in addition to the control of spark ignition timing, the engine could be operated using only intake air heating with coolant water. The results showed that the suppression of the auto-ignition timing variations among cylinders owing to the independent spark timing control of each cylinder leads to the improvement of engine output, fuel economy and exhaust emissions. Furthermore, this paper describes the engine starting and corresponding change of engine load on electric demand on generator. The stable operation could be achieved by using spark ignition, controlling of excess air ratio and intake air temperature during change the engine load from idle to rated power.

In this study, the influence of compression ratio on engine performance and variations of auto-ignition timing in each cylinder were evaluated in a 4-cycle multi-cylinder natural gas engine with PCCI combustion system. In experiment, the compression ratio was systematically changed from 19 to 25. From the result, it was clarified that an increase in compression ratio makes not only the improvement of engine output and fuel economy but also the reduction of NOx emission, even though the mechanical loss is increased. Simultaneously, the variation of auto-ignition timing in each cylinder can also be reduced.

The experimental study has been carried out on a diesel engine dual-fueled by wood-pyrolysis gas and biodiesel fuel. Wood-pyrolysis gas was simulated by a low-calorie mixed gas (LCG), which consists of hydrogen, methane and inert gas. Effects of LCG/biodiesel ratio, biodiesel injection-timing, and gas-fuel composition were examined. Obtained results show that under a constant-torque condition, an increase in gas fuel consumption causes a decrease in a brake thermal efficiency due to a decrease in combustion efficiency and specific heat ratio. Also, NOx emission in exhaust gas is decreased by increase in gas fuel consumption under the low load condition, while it shows no change under the relatively high load condition. In addition, an early injection of biodiesel is effective to reduce carbon monoxide emission due to increase in combustion pressure and temperature.

This research investigates the influences of the injection timing, injection pressure, and compression ratio on the combustion and exhaust emissions in a single cylinder 1.0 L DI diesel engine operating with ultra-high EGR. Longer ignition delays due to either advancing or retarding the injection timing reduced the smoke emissions, but advancing the injection timing has the advantages of maintaining the thermal efficiency and preventing misfiring. Smokeless combustion is realized with an intake oxygen content of only 9-10% regardless of the injection pressure. Reduction in the compression ratio is effective to reduce the in-cylinder temperature and increase the ignition delay as well as to expand the smokeless combustion range in terms of EGR and IMEP. However, the thermal efficiency deteriorates with excessively low compression ratios.

A novel EGR (exhaust gas recirculation) method by means of the intake-valve pilot-opening has been demonstrated using a single-cylinder test engine, in order to control the combustion and to reduce the energy loss due to intake-gas pre-heating in a natural gas HCCI (homogeneous charge compression ignition) engine. The intake valve, together with the exhaust valve, is slightly opened at the beginning of the exhaust stroke. Then, part of the burnt gas, which has a high temperature, is introduced into the suction pipe backward, resulting in an increase in the intake-gas temperature. The EGR rate can be varied successfully up to about 40% by using the specially designed camshaft and the valve control device, which can delay the closing timing. The effect of the EGR rate on engine performance and emissions has been investigated under the condition that the temperature of the fresh mixture and the fuel consumption rate are kept constant.

Ultra-low NOx and smokeless operation at higher loads up to half of the rated torque is attempted with large ratios of cold EGR. NOx decreases below 6 ppm (0.05 g/(kW·h)) and soot significantly increases when first decreasing the oxygen concentration to 16% with cold EGR, but after peaking at 12-14% oxygen, soot then deceases sharply to essentially zero at 9-10% oxygen while maintaining ultra low NOx and regardless of fuel injection quantity. However, at higher loads, with the oxygen concentration below 9-10%, the air/fuel ratio has to be over-rich to exceed half of rated torque, and thermal efficiency, CO, and THC deteriorate significantly. As EGR rate increases, exhaust gas emissions and thermal efficiency vary with the intake oxygen content rather than with the excess air ratio.

In our first study[1], we reported that the self-regeneration of DPF is enabled by the function of residual potassium methoxide (CH3OK) as catalyst, contained in biodiesel fuel that is collected in the DPF at lower engine loads[1]. In the present report, exhaust emission characteristics after using DPF were investigated by continuous measurement of exhaust gas. The results show that the self-regeneration of DPF occurs when engine loads change from lower to higher, and at the same time, methanol concentration in exhaust gas reaches to a higher peak. This peak is higher than when self-regeneration does not take place. The higher concentration of methanol is reduced by repeating the self-regeneration. The SOF content in PM is reduced by DPF at both high and low engine load, which is a characteristic that was not seen with gas oil.

To characterize the suitable conditions for a natural gas PCCI (premixed charge compression ignition) engine to provide both high efficiency and low emissions, an experimental study was demonstrated using a small-scale, single-cylinder engine. Engine tests were systematically carried out with various parameters, including compression ratio (18 to 22), intake-air temperature (160 to 220 °C) and engine speed (800 to 2400 rpm). It was shown that the maximum specific power can be improved in proportion to an engine speed up to 2400 rpm, while both the indicated thermal efficiency over 32% and the NOx emission below 100 ppm can be retained. However, an increase in engine speed extends the combustion duration especially under lean conditions, which decreases the indicated thermal efficiency.

The combustion characteristics in a partially premixed charge compression ignition (PCCI) engine with n-hexane were compared with ordinary diesel fuel to evaluate combustion improvements with lower distillation-temperature fuels. In the PCCI engine, a lean mixture was formed reasonably with early stage injection and the additional fuel was supplied with a second stage fuel injection after ignition. With n-hexane, thermal efficiency improved while simultaneously maintaining low NOx and smokeless combustion. A CFD analysis simulated the mixture formation processes and showed that the uniformity of the mixture with the first stage injection improves with lower distillation-temperature fuels.

The thermal cracking and polyaromatic hydrocarbon (PAH) formation processes of dimethyl ether (DME), ethanol, and ethane were investigated with chemical kinetics to determine the soot formation mechanism of oxygenated fuels. The modeling analyzed three processes, an isothermal constant pressure condition, a temperature rising condition under a constant pressure, and an unsteady condition approximating diesel combustion. With the same mole number of oxygen atoms, the DME rich mixtures form much carbon monoxide and methane and very little non-methane HC and PAH, in comparison with ethanol or ethane mixtures. This suggests that the existence of the C-C bond promotes the formation of PAH and soot.