Makoto Ikegami

A study of hydrogen fuelled compression ignition engines

Abstract The possibility of establishing a hydrogen fuelled compression ignition engine has been investigated experimentally using a conventional swirl chamber diesel engine. Two different attempts are included in this work; one dealing with the compression ignition on an air-aspirated engine system, and another with an engine operating with an argon-oxygen charge. In the former, the effect of preliminary fuelling was clarified in detail. It has been suggested that both pilot injection and fuel leakage from the injector can aid ignition of the hydrogen fuel, bringing about a smooth operation. A discussion is given of the mechanism of stabilizing ignition, from the viewpoint of thermal interactions between the engine cycles. In the latter attempt, a closed-cycle engine system is oriented and has been simulated by supplying a 21% oxygen containing mixture to the test engine. The result has indicated that ignition and engine operation are satisfactory without any ignition aid. A considerable gain has also been proved in thermal efficiency of using the argon mixture. Also, the practical feasibility of a closed-cycle compression ignition engine has been discussed.

Turbulence Intensity and Spatial Integral Scale During Compression and Expansion Strokes in a Four-Cycle Reciprocating Engine

A laser homodyne technique is applied to measure turbulence intensities and spatial scales during compression and expansion strokes in a non-fired engine. By using this technique, relative fluid motion in a turbulent flow is detected directly without cyclic variation biases caused by fluctuation in the main flow. Experiments are performed at different engine speeds, compression ratios, and induction swirl ratios. In no-swirl cases the turbulence field near the compression end is almost uniform, whereas in swirled cases both the turbulence intensity and the scale near the cylinder axis are higher than those in the periphery. In addition, based on the measured results, the k-epsilon two-equation turbulence model under the influence of compression is discussed.

A Multidimensional Model Prediction of Heat Transfer in Non-Fired Engines

An axisymmetric three-dimensional model for in-cylinder processes has been applied to the predictions of wall heat transfer in a non-fired engine cylinder. Computed heat fluxes are shown for combustion chambers with a flat piston and a deep-bowl piston for swirl and non-swirl cases. The predictions compare well with existing experimental heat fluxes at several different radii on a cylinder head except in a central part. It is also shown that the predictions of surface-averaged heat flux are consistent with those obtained from empirical correlations. The effect of compression-expansion work is indicated by predicted temperature profiles and typically demonstrated by phase difference between the heat flux and the bulk-mean gas temperature. Computational discussions are given on local heat fluxes in the deep-bowl-piston combustion chamber and suggest that local heat fluxes are greatly increased by squish motion, squish-induced vortex, and swirling motion spun-up in the bowl.

Combustion and Pollutant Formation in an Indirect Injection Diesel Engine

A traversed fast-sampling technique has been applied to explore the processes of combustion and pollutant formation in an indirect injection, swirl chamber type diesel combustion system. To permit traversed gas-sampling in each chamber, experiments were made on a double-scavenged two-stroke cycle engine with a simulated two-dimensional chamber configuration. Parameters of interest in the experiments include the extent of fuel rich zones and their decay with time, the action of swirling air motion, nitric oxide formation, the formation of hydrocarbons and soot, the state of gas outflow from the swirl chamber into the main chamber, and flame spread within the main chamber. The effect of certain operating conditions and design parameters, such as overall fuel-air ratio, injection timing, connecting passage dimension, and fuel spray direction on experimental parameters were investigated.

A stochastic approach to model the combustion process in direct-injection diesel engines

To allow description of the diesel combustion process in high-speed direct-injection diesel engines, a stochastic model consisting of the spray submodel and the combustion submodel is proposed. In each submodel, generation of turbulence and turbulent mixing of fuel and air are taken into account, and the heterogeneity and its devolution are described using the Curl collision-redispersion model. The spray is modeled on the assumption that formation of a combustible mixture during the ignition delay is controlled by turbulent mixing, not by vaporization. It is also assumed that micromixing takes place in a uniform isotropic spray region in the downstream of the spray, in which the fuel and the entrained air will accumulate. It has been shown that the predicted heat liberation at ignition is satisfactorily reproduced for a wide variety of operating conditions. The combustion submodel is basically an extension of the stochastic model proposed earlier by the present authors. Turbulence kinetics are included, in which as the source of turbulence the mechanical work done by expansion due to the heat liberation is taken into consideration. A comparison between the predicted and the measured results shows that the combustion model linked with the spray submodel can reproduce the entire course of the rate of heat release fairly well for a wide range of operating conditions. It is further shown that the model can predict the exhaust nitric-oxide concentration to a reasonable degree.

Diesel Combustion and the Pollutant Formation as Viewed from Turbulent Mixing Concept

The combustion process in high-speed direct-injection diesel engines is characterized by random turbulent mixing between turbulent eddies having different fuel concentrations. Nitric oxide and soot are formed in hot eddies and fuelrich eddies. In the present study, the authors elucidate the diesel combustion process, from the viewpoint of such heterogeneity and turbulent mixing, by analysis of high-speed flame photographs

A STUDY OF SOLUBLE ORGANIC FRACTIONS IN PARTICULATES EMITTED FROM A HIGH-SPEED DIRECT-INJECTION DIESEL ENGINE

The soluble organic fraction (SOF) of particulates emitted from a high-speed four-cycle DI diesel engine at various loads for commercial diesel fuels and some blended and distillate fuels is studied under steady operating conditions. The fuels examined have various final boiling points and aromatic contents. Emissions of lubricant, fuel fractions, and combustion products in the SOF are evaluated by chemical analysis. Exhaust emission data indicates that the addition of aromatic hydrocarbons to fuel does not cause increases in SOF or in solid fraction, and that heavier components of fuel are responsible for high level of SOF emission at medium load mainly due to the deposition of fuel on the wall of the piston cavity. Flow reactor experiments under atmospheric pressure have been conducted to look at the temperature effect of forming SOF. The results successfully explain the dependence of SOF emission on load and fuel properties. (A) For the covering abstract see IRRD 865952.

TREND AND ORIGINS OF PARTICULATE AND HYDROCARBON EMISSION FROM A DIRECT-INJECTION DIESEL ENGINE

A systematic study on particulate mass emission from a high-speed direct-injection diesel engine was conducted using a mini-dilution sampling method. Effects of fuel-air equivalence ratio, engine speed, injection timing, and swirl intensity are presented and discussed with special regard to soluble organic fraction (SOF) and hydrocarbons. Results show that these concentrations are greatly affected by ignition delay or by temperature level in the engine cylinder. As the sources of SOF and hydrocarbons, local and bulk quenching of the charge, interaction of the fuel spray with the combustion chamber walls, and slow thermal decomposition of fuel are considered and discussed. Among them, the significance of the fuel decomposition is pointed out, by separate experiments on a simulated engine by using an in-cylinder gas-sampling technique. The proposed mechanism is that at low air temperature, thermal cracking is too slow for the injected fuel to be fully decomposed, resulting in the accumulation of raw and partially cracked fuel.

Gas-Flow Measurements in a Jet Flame Using Cross-Correlation of High-Speed Particle-Images.

Time changes of a two-dimensional distribution of velocities in a nitrogen jet and a methane jet flame are measured by cross-correlation particle-image-velocimetry (PIV). From the measured results in a jet and a jetting flame, it is shown that the velocity gradient at shear layer in the reacting zone is increased due to the local acceleration by buoyancy, resulting in higher turbulence intensities compared with those in a non-reacting jet. Also, from the change of the distribution of velocity vectors with time, it is observed that the turbulence eddies are carried downstream along the gas motion with a little transformation. The time scale of turbulence at every location in the flow is obtained from the autocorrelation function of the velocity fluctuations. Furthermore, this can afford to estimate the turbulence length-scale. It is shown that the characteristic length-scales of a flaming jet are about 1.5 times greater than those of a non-flaming jet.

Turbulence Production in a Jet Assessed by the Time-Repetitive Measurement of Instantaneous Velocity Distributions.

Cross-correlation PIV is repetitively applied to obtain the time-change of instantaneous velocity vectors, which enables us to analyze turbulence kinetics. Each term in the balance equation of turbulence energy is evaluated, based on the ensembles of fluctuating velocities and instantaneous velocity-gradients, thereby finding primary factors of production and dissipation of turbulence energy. It is shown that turbulence production rate is high in the shear layer because of a large Reynolds stress, and viscous dissipation of turbulence energy occurs mainly near the jet axis. Furthermore, typical turbulence eddies in the shear layer are sampled to discuss the effect of instantaneous vortex-motions and fluctuating flows on turbulence production. It is observed that the pair of counter-rotating vortices appears and accelerates the flow in between, resulting in an increase in quantities of instantaneous Reynolds stress at a particular direction.