Search Results

The purpose of this study is to determine a pilot injection control strategy for the improvement of dual-fuel combustion with a lean natural gas/air mixture. Experiments were performed using a single cylinder test engine equipped with a common-rail injection system. The injection pressure, timing and quantity were varied at a fixed overall equivalence ratio of 0.5. The results of single-stage-injection experiments show that middle injection timings (−20 to −10 degATDC) produce low emissions of unburned species, because the pilot-fuel vapor spreads into the natural-gas lean mixture and raises the effective equivalence ratio, which leads to fast flame propagation. Early injection (−35degATDC) is advantageous for low NOx emission; however, increased emissions of unburned species are barriers.

The present study aims to obtain a strategy for optimizing the combination of injection conditions and combustion chamber geometry to achieve low carbon monoxide (CO), nitrogen oxides (NOx) and smoke emissions with high thermal efficiency at low loads in direct-injection premixed charge compression ignition (DI-PCCI) operation in a diesel engine. To this end, experiments were performed using a naturally-aspirated single-cylinder DI diesel engine equipped with a common-rail injection system and a cooled exhaust gas recirculation (EGR) system under various injection conditions, including injection timing, injection angle and injection quantity, and combustion chamber geometry. The results indicate that CO emission was reduced at injection timings that provide high peak heat release rates. To improve the NOx-CO trade-off relation, the spray angle should be properly selected depending on the combustion chamber geometry.

In this study, measurement methods of aldehydes and volatile organic compounds (VOCs) from off-road engine have been investigated. Also, their emission characteristics have been evaluated. By using high-performance liquid chromatograph (HPLC), aldehydes could be measured with small variation. Major aldehydes from off-road engine are formaldehyde and acetaldehyde. Total aldehydes emission is not necessarily low compared to THC emission. The emission characteristics of aldehydes are similar to that of CO, THC and PM. For VOCs sampling, sampling tube with absorbent was better than sampling bag because some kinds of VOCs tend to become absorbed on the sampling bag. Except for 1,3-butadiene, VOCs could be measured with small variation by using gas chromatography-mass spectrometer (GC-MS). Benzene, toluene and xylene were major species found in VOCs. The emission characteristics of VOCs were also similar to ones of CO, THC and PM.

The performance of a medium duty DME truck was evaluated by field tests and engine bench tests. The DME vehicle was given a public license plate on October 2004, after which running tests were continued on public roads and a test course. The DME vehicle could run the whole distance, about 500 km, without refueling. The average diesel equivalent fuel consumption of the fully loaded DME truck was 5.75 km/l, running at 80 km/h on public highways. Remedying several malfunctions that occurred in the power-train subsystems enhanced the vehicle performance and operation. The DME vehicle accumulated 13,000 km as of August, 2006 with no observed durability trouble of the fuel injection pump. Disassembly and inspection of the fuel injectors after 7,700 km operation revealed a few differences in the nozzle tip and the needle compared to diesel fuel operation. However, the injectors were used again after cleanup.

In this study, diesel exhaust emission characteristics were investigated as GTL (Gas To Liquid) fuel was applied to a heavy-duty diesel truck which had been developed to match a Japanese new long-term exhaust emission regulation (NOx < 2.0 g/kWh, PM < 0.027 g/kWh). The results in this study show that although the test vehicle has advanced technologies (e.g. high pressure fuel injection, oxidation catalyst, and urea-SCR aftertreatment system, etc.) which are applied to reduce diesel emissions, the neat GTL fuel has a great advantage to reduce particulate matter emissions and poly aromatic hydrocarbons. And regarding nano-size PM emissions, nuclei mode particles emitted during idling are significantly decreased by using the GTL fuel.

Formation of nitrogen oxides (NOx) in direct-injection premixed charge compression ignition (DI-PCCI) combustion simulated in a constant volume vessel was investigated using an ignition-combustion model that combines a stochastic mixing model with a reduced chemical reaction scheme. Several improvements were made to the model in order to predict the combustion processes in DI-PCCI. Calculations were carried out for the injection and ambient conditions equivalent to the measurements using the constant volume vessel. Analysis of the calculated results clarified the effects of mixture heterogeneity on NO concentrations and the mechanisms are discussed. The results show that the model successfully represents the experimental tendency for NO concentration when the injection conditions and ambient oxygen mole fraction are varied.

It has been clarified that diesel fuel properties have a great effect on the exhaust emissions and fuel consumption of a conventional diesel combustion regime. And as other diesel combustion regimes are applied in order to improve exhaust emissions and fuel consumption, it can be supposed that the fuel properties also have significant effects. The purpose of this study is to propose the optimum diesel fuel properties for a premixed compression ignition (PCI) combustion regime. In this paper, the effect of the auto-ignitability of diesel fuels on exhaust emissions and fuel consumption was evaluated using a heavy-duty single-cylinder test engine. In all experiments, fuels were injected using an electronically controlled, common-rail diesel fuel injector, and most experiments were conducted under high EGR conditions in order to reduce NOx emissions.

The combustion mechanism of a fuel droplet cloud was studied by numerical simulation. We investigated how the flame front speed and combustion products changed depending on the equivalence ratio and initial temperature. Modeling was performed using the KIVA-III software package, a three dimensional analysis software used mainly for internal combustion engine applications. The computational domain was a horizontal 1x1x100 cell sector of a spherical combustion chamber and the fuel was n-decane. Results showed that when all the fuel droplets were assumed to have evaporated, the flame front speed increased from 28 cm/s to 152 cm/s as the equivalence ratio increased. The maximum flame front speed was reached at ϕ=1.1, beyond which it decreased (at richer overall equivalence ratios). With a constant equivalence ratio, the flame front speed decreased near the outside region, because the unburned gas was compressed by the expanding burned gas.

This study aims to determine strategies for improving the relations between the pressure rise rate and emissions of nitrogen oxide (NOx), hydrocarbons (HC), and carbon monoxide (CO) in low temperature combustion (LTC) operation of a diesel engine. For this purpose, an analysis was conducted on data from experiments carried out using a single-cylinder direct-injection diesel engine with variation in the injection quantity, injection timing, exhaust-gas recirculation (EGR) rate, injection pressure, injection nozzle specification and combustion chamber geometry. The results reveal that the pressure rise rate and NOx exhibit similar tendencies when varying injection timing and EGR rate, which is opposite to CO and total HC (THC) emissions, regardless of injection quantity. When the injection quantity is increased, smoke emission becomes problematic in the selection of the injection timing.

The objective of the present study is to elucidate the combustion process of partial premixed charge compression ignition (PCCI) combustion using multiple injections in diesel engines. The effects of the ratio of the quantity of fuel used in the first and second injections, and the injection dwell time on heat release rate, soot and nitrogen oxide (NOx) formations are investigated in simulated partial PCCI combustion using a constant-volume vessel. N-heptane is used as fuel. The experiments are carried out under an ambient condition of 2 MPa and 900 K, which simulates a PCCI-like heat release rate with long ignition delays. The oxygen concentration is set to 21 and 15% to simulate conditions without and with exhaust-gas recirculation (EGR), respectively. The fuel quantity in the first injection is varied between 10 to 40% of the total fuel quantity, and the injection dwell is varied between 0.5 to 2.0 ms.

The tasks to improve diesel emissions and fuel consumption must be accomplished with urgency. However, due to the trade-off relationship between NOx emissions, soot emissions and fuel consumption, clean diesel combustion should be achieved by both innovative combustion and fuel technologies. The objective of this study is to extend the clean diesel combustion operating range (Engine-out emission: NOx ≺ 0.2 g/kWh, Soot ≺ 0.02 g/kWh). In this study, performance of a single-cylinder test engine equipped with a hydraulic valve actuation system and an ultra-high pressure fuel injection system was investigated. Also evaluated, were the effects of fuel properties such as auto-ignitability, volatility and aromatic hydrocarbon components, on combustion performance. The results show that applying a high EGR (Exhaust gas recirculation) rate can significantly reduce NOx emission with an increase in soot emission.

In this study, advantages of GTL fueled DI diesel engine were observed, then, some cautionary areas, notably the aptitude for sealing materials, were investigated. Some advantages of using GTL as a diesel engine fuel include reduction of soot emission levels, power output and fuel consumption with GTL to conventional diesel fuel operation is equivalent, super-low sulfur content of GTL and its liquid state at normal temperature and pressure. However, there are some problems with putting GTL fuel on the market, such as lubricity, aptitude for sealing materials, high cetane index and high pour point. It is necessary to use additives to improve GTL's lubricity, and selecting the most appropriate type of lubricity improver is also important. The influence of GTL on the swelling properties of standard rubber materials seem basically the same, but it is necessary to notice on used rubbers.

Since dimethyl ether (DME) is a synthetic fuel, it is possible to make it from natural gas, coal and biomass. It is a low-emission, oxygenated fuel, which does not generate soot in the exhaust. Therefore, it has recently been identified as a possible replacement for diesel fuel. In Japan, the new short-term emissions regulations will be enforced beginning in 2003, and the long-term emissions regulations are scheduled to be enforced in 2005. In order to meet these more stringent emissions regulations, existing diesel engines would not be as widely used in the near future as they currently are. This will thus bring about a more widespread use of DME engines due to their low emissions potential. Moreover, when the modification of existing diesel engines into DME engines is available at a moderate cost, the wider use of DME engines can be expected. This study targeted development and application of DME engine technology for diesel engine retrofit, in a used diesel vehicle.

In order to remove the diesel particulate matter (PM) and nitrogen oxides (NOx) from diesel exhaust, the gas is passed through a corona discharge collector for PM and another corona discharge device for NOx oxidation. With the PM collector, PM is accumulated on the central electrode, after that, it is removed by incineration technique. NOx concentration is decreased by oxidation to HNO3. In this study, these corona discharge reactors were coupled for removal of PM and NOx in progression, and attempted to remove these emissions in a slipstream of 14 liters/min of an experimental diesel engine and an actual vehicle, respectively. In case of the experimental test engine, it is found that nearly 100% and 15% of the PM and NOx emissions were removed even at a low input power of 26W (1560 J/L specific energy deposition). In the vehicle tests 1) a PM removal rate of 60% is obtained at an input power of over 40W, 2) a NOx removal rate of 97% is obtained at an input power of over 100W.

This work aimed to develop an LPG fueled direct injection SI engine, especially in order to improve the exhaust emission quality while maintaining high thermal efficiency comparable to a conventional engine. In-cylinder direct injection engines developed recently worldwide utilizes the stratified charge formation technique at low load, whereas at high load, a close-to-homogeneous charge is formed. Thus, compared to a conventional port injection engine, a significant improvement of fuel consumption and power can be achieved. To implement such a combustion strategy, the stratification of mixture charge is very important, and an understanding of its combustion process is also inevitably necessary. In this work, a numerical simulation was performed using a CFD code (KIVA-3), where the shape of a combustion chamber, swirl intensity, injection timing and duration, etc. were varied and their effects on the mixture formation and combustion process were investigated.

In this study, engine performances and exhaust emissions characteristics of compression ignition engine fueled with GTL were investigated by comparison with diesel fuel. Diesel engine could be operated fueled with GTL without any special modify for the test engine. With the high cetane number of GTL, the ignition lag was shorter, and the combustion started earlier than that of diesel fuel. Brake thermal efficiency operated with GTL increased at middle load conditions due to incomplete combustion emission such as CO and THC were lower than that of diesel fuel operation. NOx emission with GTL was comparable to diesel fuel, and there was a little decrease at high load. With GTL, soot emission was lower than with diesel fuel at above middle load condition. It seemed to be a reason of soot reduction that there was little sulphur contained in GTL.

Recently, dimethyl ether (DME) has been attracting much attention as a clean alternative fuel, since the thermal efficiency of DME powered diesel engine is comparable to diesel fuel operation and soot free combustion can be achieved. In this experiment, the effect of ambient pressure on DME spray was investigated with observation of droplet size such as Sauter mean diameter (SMD) by the shadowgraph and image processing method. The higher ambient pressure obstructs the growth of DME spray, therefore faster breakup was occurred, and liquid column was thicker with increasing the ambient pressure. Then engine performances and exhaust emissions characteristics of DME diesel engine were investigated with various compression ratios. The minimum compression ratio for the easy start and stable operation was obtained at compression ratio of about 12.

This research investigated the performance and emissions of a direct injection (DI) Diesel engine operated on 100% butane liquid petroleum gas (LPG). The LPG has a low cetane number, therefore di-tertiary-butyl peroxide (DTBP) and aliphatic hydrocarbon (AHC) were added to the LPG (100% butane) to enhance cetane number. With the cetane improver, stable Diesel engine operation over a wide range of the engine loads was possible. By changing the concentration of DTBP and AHC several different LPG blended fuels were obtained. In-cylinder visualization was also used in this research to check the combustion behavior. LPG and only AHC blended fuel showed NOX emission increased compared to Diesel fuel operation. Experimental result showed that the thermal efficiency of LPG powered Diesel engine was comparable to Diesel fuel operation. Exhaust emissions measurements showed that NOX and smoke could be considerably reduced with the blend of LPG, DTBP and AHC.

In this study, performance and emissions characteristics of an LPG direct injection (DI) engine with a rotary distributor pump were examined by using cetane enhanced LPG fuel developed for diesel engines. Results showed that stable engine operation was possible for a wide range of engine loads. Also, engine output power with cetane enhanced LPG was comparable to diesel fuel operation. Exhaust emissions measurements showed NOx and smoke could be reduced with the cetane enhanced LPG fuel. Experimental model vehicle with an in-line plunger pump has received its license plate in June 2000 and started high-speed tests on a test course. It has already been operated more than 15,000 km without any major failure. Another, experimental model vehicle with a rotary distributor pump was developed and received its license plate to operate on public roads.

As an effective method to solve the global warming and the energy crisis, the research has been carried out for the adaptability of plant oil as an alternative fuel for Diesel engine. But there are the problems of engine performance and exhaust emissions owing to the high viscosity and low volatility, when the plant oil is used as a fuel. In order to eliminate these problems, spray characteristics of the DME (Dimethyl ether) blended plant oil has been examined by using the image processing based on the shadowgraph methodology. Results show that the optimum mixing ratio of the blend is about 50:50 (by weight %). Thereafter, experiments have been conducted with a DI Diesel engine using the DME blended plant oil, and compared the exhaust emissions with Diesel, DME and transesterified fuel operation. From the results, it can be concluded that the combustion characteristics of DME blended plant oil are comparable to Diesel fuel.