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Journal Article

Combustion and Emissions with Bio-alcohol and Nonesterified Vegetable Oil Blend Fuels in a Small Diesel Engine

Combustion and exhaust gas emissions of alcohol and vegetable oil blends including a 20% ethanol + 40% 1-butanol + 40% vegetable oil blend and a 50% 1-butanol + 50% vegetable oil blend were examined in a single cylinder, four-stroke cycle, 0.83L direct injection diesel engine, with a supercharger and a common rail fuel injection system. A 50% diesel oil + 50% vegetable oil blend and regular unblended diesel fuel were used as reference fuels. The boost pressure was kept constant at 160 kPa (absolute pressure), and the cooled low pressure loop EGR was realized by mixing with a part of the exhaust gas. Pilot injection is effective to suppress rapid combustion due to the lower ignitability of the alcohol and vegetable oil blends. The effects of reductions in the intake oxygen concentration with cooled EGR and changes in the fuel injection pressure were investigated for the blended fuels.
Technical Paper

Visualization and Heat Release Analysis of Premixed Diesel Combustion with Various Fuel Ignitabilities and Oxygen Concentrations in a Constant Volume Combustion Vessel

Low NOx and soot free premixed diesel combustion can be realized by increasing ignition delays in low oxygen atmospheres, as well as the combustion here also depends on fuel ignitability. In this report single intermittent spray combustion with primary reference fuels and a normal heptane-toluene blend fuel under several oxygen concentrations in a constant volume combustion vessel was analyzed with high-speed color video and pressure data. Temperature and KL factor distributions are displayed with a 2-D two-color method. The results show that premixing is promoted with a decrease in oxygen concentration, and the local high temperature regions, above 2200 K, as well as the duration of their appearance decreases with the oxygen concentration. With normal heptane, mild premixed diesel combustion can be realized at 15 vol% oxygen and there is little luminous flame.
Technical Paper

Combustion Noise Analysis of Premixed Diesel Engine by Engine Tests and Simulations

When fuel is vaporized and mixed well with air in the cylinder of premixed diesel engines, the mixture auto-ignites in one burst resulting in strong combustion noise, and combustion noise reduction is necessary to achieve high load premixed diesel engine operation. In this paper, an engine noise analysis was conducted by engine tests and simulations. The engine employed in the experiments was a supercharged single cylinder DI diesel engine with a high pressure common rail fuel injection system. The engine noise was sampled by two microphones and the sampled engine noise was averaged and analyzed by an FFT sound analyzer. The engine was equipped with a pressure transducer and the combustion noise was calculated from the power spectrum of the FFT analysis of the in-cylinder pressure wave data from the cross power spectrum of the sound pressure of the engine noise.
Technical Paper

Improvements to Premixed Diesel Combustion with Ignition Inhibitor Effects of Premixed Ethanol by Intake Port Injection

Premixed diesel combustion modes including low temperature combustion and MK combustion are expected to realize smokeless and low NOx emissions. As ignition must be delayed until after the end of fuel injection to establish these combustion modes, methods for active ignition control are being actively pursued. It is reported that alcohols including methanol and ethanol strongly inhibit low temperature oxidation in HCCI combustion offering the possibility to control ignition with alcohol induction. In this research improvement of diesel combustion and emissions by ethanol intake port injection for the promotion of premixing of the in-cylinder injected diesel fuel, and by increased EGR for the reduction of combustion temperature.
Technical Paper

Combustion Characteristics of Emulsified Blends of Aqueous Ethanol and Diesel Fuel in a Diesel Engine with High Rates of EGR and Split Fuel Injections

Silent, clean, and efficient combustion was realized with emulsified blends of aqueous ethanol and diesel fuel in a DI diesel with pilot injection and cooled EGR. The pilot injection sufficiently suppressed the rapid combustion to acceptable levels. The thermal efficiency with the emulsified fuel improved as the heat release with the pilot injection was retarded to near top dead center, due to poor ignitability and also due to a reduction in afterburning. With the emulsified fuel containing 40 vol% ethanol and 10 vol% water (E40W10), the smokeless operation range can be considerably extended even under low fuel injection pressure or low intake oxygen content conditions.
Journal Article

Improvement in DME-HCCI Combustion with Ethanol as a Low-Temperature Oxidation Inhibitor

Port injection of ethanol addition as an ignition inhibitor was implemented to control ignition timing and expand the operating range in DME fueled HCCI combustion. The ethanol reduced the rate of low-temperature oxidation and consequently delayed the onset of the high-temperature reaction with ultra-low NOx over a wide operating range. Along with the ethanol addition, changes in intake temperature, overall equivalence ratio, and engine speed are investigated and shown to be effective in HCCI combustion control and to enable an extension of operation range. A chemical reaction analysis was performed to elucidate details of the ignition inhibition on low-temperature oxidation of DME-HCCI combustion.
Journal Article

Influence of Fuel Properties on Operational Range and Thermal Efficiency of Premixed Diesel Combustion

The influence of fuel properties on the operational range and the thermal efficiency of premixed diesel combustion was evaluated with an ordinary diesel fuel, a primary reference fuel for cetane numbers, three primary reference fuels for octane numbers, and two normal heptane-toluene blend fuels in a single-cylinder DI diesel engine. The fuel injection timing was set at 25°CA BTDC and the maximum rate of pressure rise was maintained below 1.0 MPa/°CA when lowering the intake oxygen concentration by cooled EGR. With increasing octane numbers, the higher intake oxygen concentration can be used, resulting in higher indicated thermal efficiency due to a higher combustion efficiency. The best thermal efficiency at the optimum intake oxygen concentration with the ordinary diesel fuel is lower than with the primary reference fuels with the similar ignitability but higher volatility.
Technical Paper

Dual Fuel Diesel Combustion with Premixed Ethanol as the Main Fuel

Dual fuel combustion with premixed ethanol as the main fuel and direct injection of diesel fuel as an ignition source poses problems including large unburned emissions and excessively rapid combustion. In this report the influence of compression ratios, injection timings of diesel fuel, and intake oxygen concentrations was systematically investigated in a modern diesel engine. The combustion process was classified into three stages: the first rapid combustion of diesel fuel and the ethanol mixture entrained into the diesel fuel spray; the second mild combustion with flame propagation of the ethanol mixture; and the third rapid combustion with auto-ignition of the unburned ethanol mixture without knocking. The third stage combustion occurs occasionally at several operating conditions and has been termed as PREMIER (premixed mixture ignition in the end-gas region) combustion.
Technical Paper

Improvement of Combustion and Emissions in a Dual Fuel Compression Ignition Engine with Natural Gas as the Main Fuel

Dual fuel combustion with premixed natural gas as the main fuel and diesel fuel as the ignition source was investigated in a 0.83 L, single cylinder, DI diesel engine. At low loads, increasing the equivalence ratio of natural gas to around 0.5 with intake throttling makes it possible to reduce the THC and CO emissions as well as to improve the thermal efficiency. At high loads, increasing the boost pressure moderates the combustion, but increases the THC and CO emissions, resulting in deterioration of the thermal efficiency. The EGR is essential to suppress the rapid combustion. As misfiring occurs with a compression ratio of 14.5 and there is excessively rapid combustion with 18.5 compression ratio, 16.5 is a suitable compression ratio.
Technical Paper

Optimization of Heat Release Shape and the Connecting Rod Crank Radius Ratio for Low Engine Noise and High Thermal Efficiency of Premixed Diesel Engine Combustion

Premixed diesel combustion offers the potential of high thermal efficiency and low emissions, however, because the rapid rate of pressure rise and short combustion durations are often associated with low temperature combustion processes, noise is also an issue. The reduction of combustion noise is a technical matter that needs separate attention. Engine noise research has been conducted experimentally with a premixed diesel engine and techniques for engine noise simulation have been developed. The engine employed in the research here is a supercharged, single cylinder DI diesel research engine with a high pressure common rail fuel injection system. In the experiments, the engine was operated at 1600 rpm and 2000 rpm, the engine noise was sampled by two microphones, and the sampled engine noise was averaged and analyzed by an FFT sound analyzer.
Technical Paper

Effect of Thermal Fatigue Phenomena of Aluminum Alloy by Artificial Aging

The past efforts to develop aluminum alloy engine parts were focused on the formulation of chemical composition rather than the heat treatment conditions of aluminum alloys. Only a few studies have been made on optimizing heat treatment conditions. This paper deals with the effects of artificial aging on two aluminum alloys, A356 and A319, which have been often used for engine cylinder heads. The aluminum alloys were artificially aged under several different conditions after T6 heat treatment. The alloys were tested for such mechanical properties as pure tension, cyclic loading resistance and thermo-mechanical fatigue failure. The microstructure was observed by TEM to see the effects on microstructure in terms of mechanical properties.
Technical Paper

Thermal Plastic-elastic Creep Analysis of Engine Cylinder Head

Critical for the use of aluminum alloys for cylinder heads are strength and durability. In our study, the mechanism of the low cycle fatigue and creep was clarified based on the mechanical properties of aluminum alloys, such as tensile, compressive, thermal fatigue and creep characteristics, which were determined by conducting tests on test pieces. The behavior of a cylinder head under cyclic thermal condition was represented by using a high-precision analysis method with cyclic creep taken into consideration. Moreover, the high-precision analysis method turned out to be effective in estimating a low cycle fatigue life under the cyclic thermal condition.
Journal Article

Low Temperature Premixed Diesel Combustion with Blends of Ordinary Diesel Fuel and Normal Heptane

Premixed diesel combustion blending high volatility fuels into diesel fuel were investigated in a modern diesel engine. First, various fractions of normal heptane and diesel fuel were examined to determine the influence of the blending of a highly ignitable and volatile fuel into diesel fuel. The indicated thermal efficiency improves almost linearly with increasing normal heptane fraction, particularly at advanced injection timings when the fuel is not injected directly into the piston cavity. This improvement is mainly due to decreases in the other losses, ϕother which are calculated with the following equation based on the energy balance. ηu: The combustion efficiency calculated from the exhaust gas compositions ηi: The indicated thermal efficiency ϕex: The exhaust loss calculated from the enthalpy difference between intake and exhaust gas The decreases in the other losses with normal heptane blends are due to a reduction in the unburned fuel which does not reach the gas analyzer.
Technical Paper

Semi-Premixed Diesel Combustion with Twin Peak Shaped Heat Release Using Two-Stage Fuel Injection

Characteristics of semi-premixed diesel combustion with a twin peak shaped heat release (twin combustion) were investigated under several in-cylinder gas conditions in a 0.55 L single cylinder diesel engine with common-rail fuel injection, super-charged, and with low pressure loop cooled EGR. The first-stage combustion fraction, the second injection timing, the intake oxygen concentration, and the intake gas pressure influence on thermal efficiency related parameters, the engine noise, and the exhaust gas emissions was systematically examined at a middle engine speed and load condition (2000 rpm, 0.7 MPa IMEP). The twin peak shaped heat release was realized with the first-stage premixed combustion with a sufficient premixing duration from the first fuel injection and with the second fuel injection taking place just after the end of the first-stage combustion.
Journal Article

Diesel Engine Combustion Noise Reduction by the Control of Timings and Heating Values in Two Stage High Temperature Heat Releases

Reductions in combustion noise are necessary in high load diesel engine operation and multiple fuel injections can achieve this with the resulting reductions in the maximum rate of pressure rise. In 2014, Dr. Fuyuto reported the phenomenon that the combustion noise produced in the first combustion can be reduced by the combustion noise of the second fuel injection, and this has been named “Noise Cancelling Spike Combustion (NCS combustion)”. To investigate more details of NCS combustion, the effects of timings and heating values of the first and second heat releases on the reduction of overall combustion noise are investigated in this paper. The engine employed in the research here is a supercharged, single cylinder DI diesel engine with a high pressure common rail fuel injection system.
Technical Paper

Improvements of Diesel Combustion and Emissions with Two-stage Fuel Injection at Different Piston Positions

The fuel spray distribution in a DI diesel engine with pilot injection was actively controlled by pilot and main fuel injections at different piston positions to prevent the main fuel injection from hitting the pilot flame. A CFD analysis demonstrated that the movement of the piston with a cavity divided by a central lip along the center of the sidewall effectively separates the cores of the pilot and main fuel sprays. Experiments showed that an ordinary cavity without the central lip emitted more smoke, while smokeless, low NOx operation was realized with a cavity divided by a central lip even at heavy loads where ordinary operation without pilot injection emits smoke.
Technical Paper

Time-Resolved Behavior of Unburned Hydrocarbon Components in Diesel Exhaust Under Transient Operations

Time resolved changes in unburned hydrocarbon emissions and their components were investigated in a DI diesel engine with a specially developed gas sampling system and gas chromatography. The tested transient operations include starting and increasing loads. At start-up with high equivalence ratios the total hydrocarbon (THC) at first increased, and after a maximum gradually decreased to reach a steady state value. Reducing the equivalence ratio of the high fueling at start-up and shortening the high fueling duration are effective to reduce THC emissions as long as sufficient startability is maintained. Lower hydrocarbons, mainly C1-C8, were the dominant components of the THC and mainly determined the THC behavior in the transient operations while the proportion of hydrocarbon (HC) components did not significantly change. The unregulated toxic substances, 1,3 butadiene and benzene were detected in small quantities.
Technical Paper

Cycle-to-cycle Transient Characteristics of Diesel Emissions during Starting

Changes in exhaust gas emissions during starting in a DI diesel engine were investigated. The THC after starting increased until around the 50th cycle when the fuel deposited on the combustion chamber showed the maximum, and THC then decreased to reach a steady value after about 1000 cycles when the piston wall temperature became constant. The NOx showed an initial higher peak just after starting, and increased to a steady value after about 1000 cycles. Exhaust odor had a strong correlation with THC, and at the early stage odor was stronger than would be expected from the THC concentration. The THC increased with increased fuel injection amounts, decreased cranking speeds, and fuels with higher viscosity, higher 90% distillation temperature, and lower ignitability.
Technical Paper

Ultra Low Emission and High Performance Diesel Combustion with Highly Oxygenated Fuel

Significant improvements in exhaust emissions and engine performance in an ordinary DI diesel engine were realized with highly oxygenated fuels. The smoke emissions decreased sharply and linearly with increases in oxygen content and entirely disappeared at an oxygen content of 38 wt-% even at stoichiometric conditions. The NOx, THC, and CO were almost all removed with a three-way catalyst under stoichiometric diesel combustion at both the higher and lower BMEP with the combination of EGR and a three-way catalyst. The engine output for the highly oxygenated fuels was significantly higher than that with the conventional diesel fuel due to the higher air utilization.
Technical Paper

Quantitative Measurements and Analysis of Ambient Gas Entrainment into Intermittent Gas Jets by Laser-Induced Fluorescence of Ambient Gas (LIFA)

Mixture formation processes of intermittent gas jets were visualized and quantified with high accuracy by a uniquely developed LIF technique (LIFA). Mixture strength inside gas jets was quantified by the fluorescence of iodine in the ambient gas excited by the sheet light of a Nd:YAG laser Two dimensional images of intermittent gas jets of various velocities were continuously recorded with VTR and quantified with high accuracy. The optimum conditions for measurements and accuracy with the LIFA technique were investigated. At the optimum setting of the initial iodine concentration in the ambient gas, accuracies better than 95% were obtained for the ambient gas entrainment ratio or jet concentration. The experimental results show that considerable amounts of ambient gas entrain just under the umbrella-like profile at the top of the jet. The mean jet concentration decreased with decreased nozzle diameter (D), and time elapsed after injection (Δt).