Refine Your Search



Search Results

Technical Paper

Turbulence and Cycle-by-Cycle Variation of Mean Velocity Generated by Swirl and Tumble Flow and Their Effects on Combustion

Combinations of swirl flow and tumble flow generated by 13 types of swirl control valve were tested by using both impulse steady flow rig and LDV. Comparison between the steady flow characteristics and the result of LDV measurement under motoring condition shows that tumble flow generates turbulence in combustion chamber more effectively than swirl flow does, and that swirling motion reduces the cycle by cycle variation of mean velocity in combustion chamber which tends to be generated by tumbling motion. Performance tests are also carried out under the condition of homogeneous charge. Tumble flow promotes the combustion speed more strongly than expected from its turbulence intensity measured by LDV. It is also shown that lean limit air fuel ratio does not have a strong relation with cycle variation of mean velocity but with turbulence intensity.
Technical Paper

Three-Dimensional Computation of the Effects of the Swirl Ratio in Direct-Injection Diesel Engines on NOx and Soot Emissions

Three-dimensional computation has been applied to analyze combustion and emission characteristics in direct-injection diesel engines. A computational code called TurboKIVA was used to investigate the effects of the swirl ratio, one of the fundamental factors related to combustion control, on combustion characteristics and NOx and soot emissions. The code was first modified to calculate soot formation and oxidation and the precise behavior of fuel drops on the combustion chamber wall. As a result of improving calculation accuracy, good agreement was obtained between the measured and predicted pressure, heat release rate and NOx and soot emissions. Using this modified version of TurboKIVA, the effects of the swirl ratio on NOx and soot emissions were investigated. The computational results showed that soot emissions were reduced with a higher swirl ratio. However, a further increase in the swirl ratio produced greater soot emissions.
Technical Paper

Development of a New Compound Fuel and Fluorescent Tracer Combination for Use with Laser Induced Fluorescence

Laser induced fluorescence (LIF) is a useful method for visualizing the distribution of the air-fuel ratio in the combustion chamber. The way this method is applied mainly depends on the fluorescent tracer used, such as biacetyl, toluene, various aldehydes, fluoranthene or diethylketone, among others. Gasoline strongly absorbs light in the UV region, for example, at the 248-nm wavelength of broadband KrF excimer laser radiation. Therefore, when using this type of laser, iso-octane is employed as the fuel because it is transparent to 248-nm UV light. However, since the distillation curves of iso-octane and gasoline are different, it can be expected that their vaporization characteristics in the intake port and cylinder would also be different. The aim of this study was to find a better fuel for use with LIF at a broadband wavelength of 248 nm. Three tasks were undertaken in this study.
Technical Paper

Effects of NOx and Unburned Gasoline on Low Temperature Sludge Formation in Engine Oil

It is generally known that NOx reacts with unburned gasoline, olefins in particular, to form sludge precursors. In this study, the authors investigated the process by which NOx and unburned gasoline mix into the engine oil and analyzed the mechanism whereby stop and go driving accelerates sludge formation. It has been found that NOx detected in the engine oil as nitrite ions mixes into the oil in the crankcase. The NOx concentration in the engine oil increases rapidly when the crankcase gas temperature is nearly equal to the dew point of the water vapor in the crankcase. Unburned gasoline is mainly absorbed into the oil through the oil film on the cylinder walls and the oil in the ring grooves. During low-temperature engine operation in stop-go driving (i.e., when the vehicle is stopped), NOx and unburned gasoline are absorbed into the engine oil and, in high-temperature engine operation (i.e., when the vehicle is moving), NOx and unburned gasoline are released from the oil.
Technical Paper

Development of Four Cylinder SR Engine

The SR engine is a new medium-size, all aluminum (cylinder block, head, rocker cover and oil pan) in-line 4-cylinder gasoline powerplant developed as a replacement for CA engine in Nissan's compact passenger cars. The development aim set for this engine was to achieve excellent power output and ample torque in the middle-and high-speed ranges, as well as a clear, linear engine sound up to the red zone. These performance targets have been achieved through the use of the 4-valve-per-cylinder DOHC design featuring a Y-shaped valve rocker arm system. This system allows a straight intake port for high power output and a narrow valve angle for a compact combustion chamber. The result is ample torque output as well as good fuel economy.
Technical Paper

Factors Limiting the Improvement in Thermal Efficiency of S. I. Engine at Higher Compression Ratio

An analysis of the factors that limit the improvement in thermal efficiency at higher compression ratios was performed with both thermodynamic calculation and experiment. The results showed that the major factors were cooling loss and unburned fuel. Both of these factors increase with smaller swept volume, larger S/V ratio combustion chamber, and lower engine speed and load. These effects explain the observation that thermal efficiency peaks at relatively low compression ratio.
Technical Paper

An Analytical Study on Knocking Heat Release and its Control in a Spark Ignition Engine

In this study the relationship between the timing for the onset of autoignition and the amount of mixture fraction burned by autoignition and the resulting knock intensity is investigated using a combination of high-speed laser shadowgraphy and thermodynamic calculations. It is made clear that over 40 percent of the entire mixture burns due to autoignition in a crank angle of less than five to eight degrees when an engine is operated under a heavy knocking condition. This burn rate is about ten times higher than that of combustion seen in a normally propagating flame. This abrupt heat release causes an oscillation in cylinder gases, resulting in a knocking sound. The experimental procedure is applied to examine the effect of a squish combustion chamber on suppressing knock. The results indicate that, when autoignition occurs in the squish area, an amount of mixture burned by autoignition is small, resulting in lower knock intensity.
Technical Paper

Development of a New 12 Valve 4 Cylinder Engine

The 1.5 1 GA15 engine is a new inline 4 cylinder engine. The GA15 fully meets the major development objectives of sufficient torque at low and middle engine speeds, high power output, good fuel economy and quiet engine operation. Its structure features a compact combustion chamber with a small bore and long stroke, aerodynamic intake ports, a stiff engine cylinder block with a deep skirt and bearing beam, a newly designed silentrunning chaine, and pistons with full floating pins. High quality was achieved by adopting the latest methods in its development: vibration analysis of the assembled engine and transmission, FEM model, rigidity analysis of the cylinder block and head, and analysis of air flow in the intake port and movement of the timing chain.
Technical Paper

Effect of Gasoline Composition on Engine Performance

In order to clarify the effect of each gasoline component on engine performance during warm-up, changes in the air-fuel ratio and quantity of wall flow (liquid gasoline on the induction port) were measured using ordinary gasolines and model gasolines consisting of a blend of several hydrocarbons and MTBE (methyl-tertiary-butyl-ether). The unburned air-fuel mixture in a combustion chamber was sampled via a solenoid valve and analyzed by gas chromatography to investigate the vaporization rate of each component. The results show that MTBE has an important effect on driveability because it contains oxygen and easily vaporizes, resulting in a lean mixture in the transient state. The popular driveability index, T50 (50% distillation temperature), does not provide an adequate means of evaluating MTBE-blended gasoline.
Technical Paper

Effect of Intake Valve Deposits and Gasoline Composition on S.I. Engine Performance

Valve deposits in gasoline engines increase with time, absorbing fuel during acceleration and releasing fuel during deceleration. Valve deposits insulate the heat release from the cylinder and this phenomenon is the cause of bad fuel vaporization. In this way, the deposits greatly affect the driveability and exhaust emissions. Using a 3.OL MPI(Multipoint Injection) engine, we measured the quantity of fuel that deposits at the intake port, and the throttle response (using a wall-flow meter made by Nissan Motor Co.1), 2) to study the deposits effect on driveability and exhaust emissions at a low temperature. The deposits were formed on the intake valve surface (about 8.0 on the CRC deposit rating scale) through 200 hours of laboratory engine stand operation. At low temperature, C9 and C10 hydrocarbons tend to stick to the intake port surface and intake valve as “wall-flow”; this is one cause of bad driveability.
Technical Paper

Numerical Simulation System for Analyzing Fuel Film Flow in Gasoline Engine

A new numerical simulation system has been developed which predicts flow behavior of fuel film formed on intake port and combustion chamber walls of gasoline engines. The system consists of a film flow model employing film thickness as a dependent variable, an air flow model, and a fuel spray model. The system can analyze fuel film flow formed on any arbitrary three-dimensional configuration. Fuel film flow formed under a condition of continuous intermittent fuel injection and steady-state air flow was calculated, and comparison with experimental data showed the system possessing ability of qualitative prediction.
Technical Paper

Effects of Combustion Chamber Insulation on the Heat Rejection and Thermal Efficiency of Diesel Engines

Experiments were conducted with 4-cylinder and single-cylinder direct injection diesel engines to examine the effects of combustion chamber insulation on heat rejection and thermal efficiency. The combustion chamber was insulated by using a silicon nitride piston cavity that was shrink-fitted into a titanium alloy crown. The effect of insulation on heat rejection was examined on the basis of heat release calculations made from cylinder pressure time histories. High-speed photography was used to investigate combustion phenomena. The results showed that heat rejection was influenced by the combustion chamber geometry and swirl ratio and that it was reduced by insulating the combustion chamber. However, because combustion deteriorated, it was not possible to obtain an improvement in thermal efficiency equivalent to the reduction in heat rejection.
Technical Paper

Sources of Hydrocarbon Emissions from a Small Direct Injection Diesel Engine

The purpose of this paper is to clarify the mechanisms of unburnt hydrocarbon (HC) emissions from a small direct - injection (DI) diesel engine. HC emission levels of small DI diesel engines are considerably higher than those of corresponding indirect - injection (IDI) diesel engines, even when sacless injection nozzles that are effective in reducing HC emissions are installed on them. In this study, analytical engine tests were performed to evaluate the relative significance of various potential sources of HC emissions from a small DI diesel engine equipped with sacless type injectors.
Technical Paper

Ignition, Combustion, and Exhaust Emissions of Lean Mixtures in Automotive Spark Ignition Engines

Misfire and cycle-to-cycle combustion variation are both serious problems in securing good engine performance and low exhaust emissions in the case of using extremely lean mixtures. Making some modifications in the ignition system and in the combustion chamber, and increasing the mixture turbulence, we examined their effects upon the lean limit, the engine performance, and the exhaust emissions. It was found that gap width and gap projection of a spark plug and spark energy as well as mixture turbulence had a great effect on extending the lean limit and improving engine performance with lean mixtures. A compact combustion chamber is preferable for lean mixture operation. Smooth operation of the engine can be maintained even at retarded spark timing by applying the above-mentioned items and providing hot intake air to the engine. Consequently, exhaust emissions, including hydrocarbons and oxides of nitrogen, can be substantially reduced.
Technical Paper

Analytical Study on Engine Vibration Transfer Characteristics Using Single-Shot Combustion

In order to demonstrate the generation mechanism of “combustion noise” separately from “mechanical noise,” the process of transfer in which vibration travels to each engine portion was analyzed through single-shot combustion of a propane-air mixture in the combustion chamber with the crankshaft fixed at a given angle. The effect of the natural frequency of each portion of the engine on the vibration transfer characteristics is discussed by introducing a vibration transfer function. The transfer paths of exciting forces which are caused by the combustion are quantitatively clarified.
Technical Paper

Stabilized Combustion in a Spark Ignited Engine through a Long Spark Duration

An investigation has been done on the relationship between spark ignition characteristics and combustion stability in a gasoline engine. The spark discharge parameters examined were the spark current, energy, and duration. It has been found that lengthening the spark discharge duration is particularly effective in achieving stabilized combustion. A longer spark duration provides a continued supply of electric energy as kinetic energy to the mixture around the spark gap. The analytical results of a constant volume combustion chamber test verify that a longer spark duration promotes flame initiation and makes reliable flame propagation possible. The length of the spark duration is regarded as the period from ignition to the onset of combustion pressure rise. The results of a combustion pressure analysis reveal that the spark duration must be longer than the heat release delay.
Technical Paper

Characteristics of Mixture Formation in a Direct Injection SI Engine with Optimized In-Cylinder Swirl Air Motion

This paper presents a study of mixture formation in the combustion chamber of a direct-injection SI engine. In-cylinder flow measurement was conducted using laser Doppler velocimetry (LDV) and particle image velocimetry (PIV), and visualization of fuel vapor behavior was done using laser-induced fluorescence (LIF). Further, fast response flame ionization detector (FID) was used to measure the hydrocarbon (HC) concentrations in the vicinity of the spark plug. Thereby mixture concentrations in the vicinity of the spark plug, within the mixture distribution observed using LIF, were quantified. Results revealed that an upward flow forms near the center of the cylinder in the latter half of the compression stroke and goes from the piston crown toward the cylinder head. This upward flow is caused by the synergistic effect of the swirl motion generated in the cylinder and the cylindrical bowl provided in the piston crown eccentrically to the central axis of the cylinder.
Technical Paper

A Study of Heat Rejection and Combustion Characteristics of a Low-temperature and Pre-mixed Combustion Concept Based on Measurement of Instantaneous Heat Flux in a Direct-Injection Diesel Engine

There have been strong demands recently for reductions in the fuel consumption and exhaust emissions of diesel engines from the standpoints of conserving energy and curbing global warming. A great deal of research is being done on new emission control technologies using direct-injection (DI) diesel engines that provide high thermal efficiency. This work includes dramatic improvements in the combustion process. The authors have developed a new combustion concept called Modulated Kinetics (MK), which reduces smoke and NOx levels simultaneously by reconciling low-temperature combustion with pre-mixed combustion [1, 2]. At present, research is under way on the second generation of MK combustion with the aim of improving emission performance further and achieving higher thermal efficiency [3]. Reducing heat rejection in the combustion chamber is effective in improving the thermal efficiency of DI diesel engines as well as that of MK combustion.
Technical Paper

Modeling and Measurement on Evaporation Process of Multicomponent Fuels

In previous multi-dimensional modeling on spray dynamics and vapor formation, single component fuel with pure substance has been analyzed to assess the mixture formation. Then it should be expected that the evaporation process could be performed for the multicomponent fuel such as actual Gasoline and Diesel gas oil. In this study, vapor-liquid equilibrium prediction was conducted for multicomponent fuels such as 3 and 10 components mixed solution with ideal solution analysis and non-ideal solution analysis. And the computation of distillation characteristics was conducted for the steady state fuel condition fuel condition to understand the evaporation process. As a result, calculated distillation characteristics are consistent well with experiment results. And the evaporation process of a multicomponent droplet in the combustion chamber has been calculated with the variation of ambient pressure and temperature.
Technical Paper

In-Cylinder Temperature Distribution Measurement and Its Application to HCCI Combustion

This paper presents a measurement technique to visualize the distribution of the in-cylinder mixture temperature and an experimental approach for analyzing the effect of the temperature distribution prior to ignition on homogeneous charge compression ignition (HCCI) combustion. First, a visualization technique for mixture temperature distribution based on the temperature dependence of laser induced fluorescence (LIF) was developed. As the next step, measurement of the temperature distribution was applied to an analysis of HCCI combustion. Controlled non-uniform temperature distributions in the mixture prior to ignition were generated by a special intake system with a completely divided intake port having separate electrical heaters.