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A novel total hydrocarbon (THC) emission concentration estimation model is proposed for reduction of engine development cost and simplification of exhaust measurements. The proposed method uses the absorbance spectra of a Fourier transform infrared (FTIR) spectrometer, which contains the information on a wide variety of hydrocarbons, as input. The model is based on machine learning algorithms including the least absolute shrinkage and selection operator (LASSO) regression and bagging techniques. To train the model, we created a dataset containing pairs of a spectrum of engine exhaust gas and the THC concentration. In addition, we incorporate absorbance spectra of individual hydrocarbon components and several inorganic components so that the model learns the contribution of each hydrocarbon to THC concentration and to ignore interferences of irrelevant gas components.

For the measurements of flow rate, pressure and/or temperature in an engine exhaust pipe, probes are often inserted into the exhaust pipe depending on the application. These measurement probes differ a lot in terms of their size and shape. The flow around the probes become further complicated due to the pulsation of engine exhaust flow. In this study, computational fluid dynamics (CFD) simulations were carried out and a zero-dimensional (0D) model was constructed to analyze the flow field around the probe and flow rate of a pulsating flow. The simulations and the measurements of the flow rate and pressure were performed on flows around a hexagonal prism inserted in a circular pipe which is intended to be a differential pressure flow meter. The velocity field was also measured using the particle image velocimetry (PIV) technique. The CFD simulation results were validated with the experiments for both steady and pulsating flows.

This report describes the implementation of the spark channel short circuit and blow-out submodels, which were described in the previous report, into a spark ignition model. The spark channel which is modeled by a particle series is elongated by moving individual spark particles along local gas flows. The equation of the spark channel resistance developed by Kim et al. is modified in order to describe the behavior of the current and the voltage in high flow velocity conditions and implemented into the electrical circuit model of the electrical inductive system of the spark plug. Input parameters of the circuit model are the following: initial discharge energy, inductance, internal resistance and capacitance of the spark plug, and the spark channel length obtained by the spark channel model. The instantaneous discharge current and the voltage are obtained as outputs of the circuit model.

A series calculation methodology from the injector nozzle internal flow to the in-cylinder fuel spray and mixture formation in a diesel engine was developed. The present method was applied to a valve covered orifice (VCO) nozzle with the recent common rail injector system. The nozzle internal flow calculation using an Eulerian three-fluid model and a cavitation model was performed. The needle valve movement during the injection period was taken into account in this calculation. Inside the nozzle hole, cavitation appears at the nozzle hole inlet edge, and the cavitation region separates into two regions due to a secondary flow in the cross section, and it is distributed to the nozzle exit. Unsteady change of the secondary flow caused by needle movement affects the cavitation distribution in the nozzle hole, and the spread angle of the velocity vector at the nozzle exit.

In direct-injection (DI) gasoline engines, spray characteristics greatly affect engine combustion. For the rapid development of new gasoline direct-injectors, it is necessary to predict the spray characteristics accurately by numerical analysis based on the injector nozzle geometry. In this study, two-phase flow inside slit nozzle injectors is calculated using the volume of fluid method in a three-dimensional CFD. The calculation results are directly applied to the boundary conditions of spray calculations, of which the submodels are recently developed to predict spray formation process in direct injection gasoline engines. The calculation results are compared with the experiments. Good agreements are obtained for typical spray characteristics such as spray shape, penetration and Sauter mean diameter at both low and high ambient pressures. Two slit nozzle injectors of which the slit thickness is different are compared.

A three-dimensional numerical model has been developed to predict spray formation process of swirl or slit type injectors which are currently used in direct-injection gasoline engines. The Discrete Droplet Model (DDM) is totally enhanced: a new droplet deformation model is developed, which is theoretically introduced with a spheroidal shape assumption. The droplet drag model and droplet break-up model via Kelvin-Helmholtz and Rayleigh-Taylor instabilities are modified taken into account with the deformation. The break-up model parameters are dynamically changed according to a droplet Weber number. The model functions are developed using single droplet breakup measurement data. A liquid sheet injection and breakup models are incorporated into the DDM. A new parcel radius model is also introduced to get rid of the grid dependence of the droplet collision-coalescence model.

A multi-component fuel vaporization model is developed for numerical analysis of specific fuel component behaviors in port-fuel-injection(PFI) gasoline engines. In order to specify the differences of in-cylinder fuel distribution among its components, three-dimensional calculations of intake flow, spray and vapor motion of each component are performed with respect to engine wall temperature and the distillation characteristics of the fuel. Simultaneous measurements of in-cylinder behaviors of different volatility components in the fuel are also carried out using a laser-induced fluorescence (LIF) technique to validate the calculation results. In both measurements and calculations, the same fuels are used, which are composed of seven or eight components to simulate the distillation characteristics of two kinds of gasoline. The in-cylinder vapor amount of high and low volatility components is compared between the calculations and the experiments.

Three-dimensional numerical analysis of fuel liquid and mixture behavior in a port-injection gasoline engine is assessed by comparing calculations with measurements. The fuel mass distributed in the intake port and cylinder is measured using an engine with hydraulic valve and gas sampling system. The experimental results show that about half of the fuel mass per injection enters the cylinder, and the rest stays in the port. The difference of the mass fraction of injected fuel directly entering the cylinder is small between the cases of single pulse injection and serial injection. Therefore, three-dimensional calculation presupposing single pulse injection has difficulty in predicting the in-cylinder mixture formation process, although it can analyze the amount of fuel wetting the port wall. The calculations are performed for a port-injection engine, and the differences of fuel behavior with respect to swirl control valve opening and wall temperature are discussed.

A new spray/wall impingement model for gasoline engines has been developed. The model is based on experimental analysis of impinging spray droplets using a phase doppler particle analizer (PDPA). Three new equations were obtained in terms of droplet size, Weber number and the angle from a wall for droplets which were splashed after impinging or created by the impact of a droplet on the liquid film layer on the wall. The three-dimensional calculation results using the model agree very well with the experimental data. The model is also applied to the fuel mixture formation process in a lean-burn gasoline engine.

Soot formation process was examined by high speed photographs, using a single cumbustion diesel engine with a transparent swirl chamber. Fuel-air mixture and flames, and soot clouds were visualized by the schlieren method and the back-illuminated method, respectively. A three dimensional simulation program with soot formation and oxidation models was developed to clarify diesel soot formation processes. The models consist of several models previously proposed and partly improved in this study. Good agreement was obtained between calculated and experimental results. The following points were clarified through observation and numerical studies: (1) The main soot area is considerably smaller than luminous flame area, especially in the initial soot formation process. (2) The main soot cloud first appears in the tip region of fuel-air mixture, downstream of ignition position a few submilliseconds after the ignition.

In order to optimize air-fuel mixture formation in a small DI diesel engine, studies were conducted into the effects of combustion chamber shape and fuel spray impingement. Based on the findings of these studies, the shape of the combustion chamber was modified to induce complex air motion with high turbulence and fuel injection was carefully controlled to achieve optimum impingement intensity. As a result, the mixture formation process was greatly improved with a consequent gain in terms of engine performance. To clarify the reasons for this improvement in combustion, a three-dimensional calculation of the in-cylinder air motion was made. The behaviour of the spray and flame was observed using an endoscope. The new combustion system, named TOYOTA Reflex Burn system (TRB) thus developed has been adopted in production engines since August 1988.