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In a motorcycle gasoline engine, the port fuel injection system is rapidly spread. Compared to an automotive engine, the injected fuel does not impinge on the intake valve due to space restriction to install the injector. In addition, as the air flow inside the intake pipe may become very fast and has large cycle-to-cycle variation, it is not well found how the injector should be installed in the intake pipe to prepare “good” fuel-air mixture inside the intake pipe. In this study, the formation process of the fuel-air mixture is measured by using ILIDS system that is a 2-D droplets' size and velocity measurement system with high spatial resolution. Experiments with changing conditions such as flow speed and injection direction are carried out. As a result, the effects of injection direction, ambient flow speed and wall roughness on the fuel-air mixture formation process was examined, considering the three conditions of cold start, light to medium load operation and high load operation.

Low temperature plasma ignition has been proposed as a new ignition technique as it has features of good wear resistance, low energy release and combustion enhancement. In the authors’ previous study, lean burn limit could be extended slightly by low temperature plasma ignition while the power supply’s performance with steep voltage rising with time (dV/dt), showed higher peak value of the rate of heat release and better indicated thermal efficiency. In this study, basic study of low temperature plasma ignition system was carried out to find out the reason of combustion enhancement. Moreover, the durability test of low temperature plasma plug was performed to check the wear resistance.

The objective of this study is to develop a practical technique to achieve HCCI operation with wide operation range. To attain this objective, the authors previously proposed the blowdown supercharge (BDSC) system and demonstrated the potential of the BDSC system to extend the high load HCCI operational limit. In this study, experimental works were conducted with focusing on improvement of combustion stability at low load operation and the reduction in cylinder to cylinder variation in ignition timing of multi-cylinder HCCI operation using the BDSC system. The experiments were conducted using a slightly modified production four-cylinder gasoline engine with compression ratio of about 12 at constant engine speed of 1500 rpm. The test fuel used was commercial gasoline which has RON of 91. To improve combustion stability at low load operation, the valve actuation strategy for the BDSC system was newly proposed and experimentally examined.

A direct injection gasoline engine system which employs a unique combustion system with enhanced gas motion is evaluated. Enhanced gas motion is produced by employing both a moderately strong swirl flow and a cavity in the piston. Advantages of this system are that the injection timing or spark timing need not be controlled severely and that since the injection timing can be set at near the intake BDC, time for evaporation can be gained to reduce soot emissions. Problems to be improved are that the Nox emissions level is worse than other lean burn systems and full load operation is not evaluated. According to the numerical calculations, the problems may be solved by enhancing the in-cylinder gas motion with axial stratification of swirl intensity at intake BDC; strong swirl near the cylinder head and weak swirl near the piston surface.

In this study, the characteristics of diesel spray droplets, such as the velocity and the diameter were simultaneously measured by using an improved ILIDS (Interferometric Laser Imaging for Droplet Sizing) method on a 2D plane to evaluate the droplet breakup modeling. In numerical analysis, DDM (Discrete Droplet Model) was employed with sub-models such as droplet breakup, droplet drag force and turbulence. Experiments have been performed with an accumulator type unit-injector system and a constant-volume high-pressure vessel under the condition of quiescent ambient gas. The injection pressure and ambient gas pressure were set up to 100 MPa and 0.1 / 1 MPa, respectively. The nozzle orifice diameter was 0.244 mm with a single hole. The measurement region was chosen at 40 ∼ 60 mm from the nozzle-tip. Numerical analysis of diesel sprays was conducted and the results were compared to the measured results.

In order to measure the spatial distribution of fuel jet concentration quantitatively, a technique combining methods of fluorescence with absorption was developed. LIF method can obtain the spatial fuel distribution qualitatively, but quantitative measurement is difficult. Meanwhile, laser-beam absorption method can quantitatively obtain the integrated jet concentration on the light-path. In addition, scanning the laser-beam allows for a quasi 2-D quantitative measurement of the jet concentration. Firstly, in this study, this measurement system was tested in a homogeneously charged field while varying the dopant NO2 concentration, the laser-beam scanning speed, and the ambient pressure. As a result, some data-correction techniques were developed to produce a quantitative measurement. Secondly, this system was applied to gaseous jet fields in a constant volume bomb.

The authors have been engaged in developing a new-generation two-stroke gasoline engine which could be employed ultimately for automobiles. By investigating the defects of the Schnurle-type two-stroke gasoline engine, a reverse uniflow-type direct injection engine has been developed and built. The newly introduced system employs stratified charge combustion in light to medium load conditions by using the technology already developed for the four-stroke direct injection gasoline engines while it can supply the maximum power output by using a super-charger and attaining homogeneous combustion. Engine performance is being tested experimentally. In order to analyze the performance test results, numerical analysis of in-cylinder phenomena, such as gas-exchange, gas motion, fuel spray formation, and mixture formation is carried out in this paper.

A Direct Injection Stratified Charge Rotary Engine ( DISC-RE ) with a pilot flame ignition system has been studied to find the possibility of simultaneous reductions of fuel consumption rate and HC exhaust gas emissions. Firstly, combustion characteristics in a model combustion chamber, which simulates the DISC-RE were examined from the viewpoints of calculation and experiment. The high speed photography and the indicated pressure analysis were experimentally performed while numerical calculations of the mixture formation and combustion processes were also carried out. As a result, it has been found that the combustion using the pilot flame ignition system is much activated and a better ignitability is attained under lean mixtures than using a spark ignition system. Secondly, a single rotor with 650 cc displacement DISC-RE was built as a prototype. Combustion characteristics and its performance were tested using a combustion analyzer.

To clarify the fuel spray formation process for a swirl-type injector, numerical analyses using both VOF (Volume Of Fluid) model and DDM (Discrete Droplet Model) method are carried out. VOF model is used to simulate the two-phase flow inside the injector and also the liquid film formation process outside the nozzle, while DDM is used to simulate a free fuel spray in a constant-volume chamber using initial conditions deduced by empirical equations or calculated results of VOF model. As a result, fairly good agreement of spray characteristics, such as the spray shape and the tip penetration between the experiment and calculation can be obtained by adopting initial conditions calculated by VOF model. However, improvements of droplet breakup models and of two-phase flow calculation method would be required to achieve quantitatively good agreement.

Knocking occurs within the high-speed range of small two-stroke engines used in handheld work equipment. High-speed knock may be affected by the engine speed and delivery ratio. However, evaluation of these factors independently using experimental methods is difficult. Therefore, in this study, these factors were independently evaluated using numerical calculations. The purpose of this study was to clarify the mechanism by which the intensity of high-speed knocking that occurs in small two-stroke engines becomes stronger. The results suggest that temperature inhomogeneity due to insufficient mixing of fresh air and previously burned gas may induce high-speed knocking in the operating range at high engine speeds.

The phenomenon of autoignition is an important aspect of HCCI and knock, hence reliable information on local gas temperature in a combustion chamber must be obtained. Recently, several studies have been conducted by using laser techniques such as CARS. It has a high spatial resolution, but has proven difficult to apply in the vicinity of combustion chamber wall and requires special measurement skills. Meanwhile, a thermocouple is useful to measure local gas temperature even in the vicinity of wall. However, a traditional one-wire thermocouple is not adaptable to measure the in-cylinder gas temperature due to slow response. The issue of response can be overcome by adopting a two-wire thermocouple. The two-wire thermocouple is consisted of two fine wire thermocouples with different diameter hence it is possible to determine the time constant using the raw data from each thermocouple.

A new idea for controlling the in-cylinder mixture formation in SI engines is proposed. This concept was developed by applying the results of numerical calculations. Fuel that is directly injected into the cylinder is transferred toward the cylinder head to form a mixture stratification by using the in-cylinder gas motion that is generated by the interaction between the swirl and squish flows inside a combustion chamber. At first, the flow characteristics were measured in the whole in-cylinder space using an LDV system. Also, numerical calculations of the in-cylinder flow were made using measured data as the initial conditions. Secondly, the local equivalence ratio at several points inside the combustion chamber was measured by using a fast gas sampling device.

Low temperature plasma ignition has been proposed as a new ignition technique as it has features of good wear resistance, low energy release and combustion enhancement. In the authors’ previous study, lean burn limit could be extended by low temperature plasma ignition while a voltage drop during discharge, leading to the transition to arc discharge, was found. In this study, the structure of plug and power supply’s performance with steep voltage rising with time, dV/dt, are examined to investigate the effects on combustion performance. As a result, comparing three power sources of conventional, IES and steep dV/dt, steep dV/dt showed small cycle-to-cycle variation and shorter combustion period, leading to higher peak value of the rate of heat release and better indicated thermal efficiency by relatively 6% and 4% compared to CIC and IES, respectively.

The purpose of this paper is to find a way to extend the high load limit of homogeneous charge compression ignition (HCCI) combustion. This paper presents the effect of in-cylinder flow and stratified mixture on HCCI combustion by experiments and three-dimensional computer fluid dynamics coupled with a detailed chemical reaction calculation. The first study was conducted using a rapid compression and expansion machine (RCEM) equipped with a flow generation plate to create in-cylinder turbulent flow and with a control unit of in-cylinder wall temperature to create in-cylinder temperature distribution. The study assesses the effect of the turbulent flow and the temperature distribution on HCCI combustion. In the second study, the numerical simulation of HCCI combustion was conducted using large eddy simulation coupled with a detailed chemical reaction calculation. The study analyzes the interaction between in-cylinder turbulent flow and mixture distribution and HCCI combustion.

Resistive particulate matter sensor (PMS) is a promising solution for the diagnosis of diesel/gasoline particulate filter (DPF/GPF) functionality. Frequently triggered regeneration of their sensing element, for cleaning the soot dendrites deposited on the surface, leads to experience high temperature and thermal stress and pose high risk of developing cracks in the electrodes or sensing substrate. A semiconductor with a dopant concentration of 100 ppm~10000 ppm is applied as a sensing element for PMS self-diagnosis. Upon cooling at air, the polarization doped-insulating layer in a resistive PMS starts to resume the electrical conductivity in the wake of experiencing high regeneration temperature, through the electron and hole directional mobility.

The effect of properties of lubricating oil on low speed pre-ignition (LSPI) was investigated. Three different factors of oil properties such as cetane number, distillation characteristics and Calcium (Ca) additive (with and without) are prepared and examined. Then actual engine test of LSPI was carried out to evaluate the effect and to clarify the mechanism and role of lubricating oil. Finally it is clarified that the oil cetane number and/or Ca additive strongly affect LSPI phenomena.

The analysis of spray characteristics is important to examine the combustion characteristics of DI (Direct Injection) gasoline engines because the fuel-air mixture formation is controlled by spray characteristics and in-cylinder gas motion. However, the mixture formation process has not been well clarified yet. In this study, the characteristics of a fan-shaped spray caused from a slit-type injector, such as the droplet size, its velocity and the droplet distribution were simultaneously measured on a 2D plane by using improved ILIDS (Interferometric Laser Imaging for Droplet Sizing) method. ILIDS method is an optical measurement technique using interference fringes by illuminating a transparent spherical particles with a coherent laser light. In the measurement of the wall-impinging spray, effects of the distance to the wall and the wall temperature on the spray characteristics were investigated.

A reverse uniflow-type two-stroke gasoline direct injection engine, which has potentials of high power weight ratio, high thermal efficiency and low exhaust gas emissions, has been developed and tested. In this study, one of the features of this engine: very low cycle-to-cycle combustion variation at idling condition, is focused to clarify the reasons. To achieve this, a transparent cylinder model engine was designed and built to visualize the in-cylinder mixture formation process, and the free spray characteristics of a swirl-type injector were examined using a large chamber with changing the injection pressure, environmental gas pressure, and the gas temperature. As a result, the reasons of stable idling operation were deduced.

Porous materials, which have large surface areas, have been used for heat storage. However, porous Si-SiC material, as heat storage medium to be applied to a turbocharged gasoline engine has not been investigated extensively. In this study, porous Si-SiC material was used in the upstream of the turbine as heat storage medium and a model was thereby developed for further study. Substrate surface area and substrate volume of Si-SiC were calculated for structure model calibration. Following these calculations and test results, the pressure loss and thermal model were validated. Results show that the weaken exhaust gas pulsation amplitude by porous Si-SiC leads to better turbine performance and BSFC in steady engine condition for a turbocharged gasoline engine. In addition, its transient operation response needs to be improved under transient engine conditions. Hence the possibility of improving the transient response is investigated with characteristics of porous Si-SiC material.

PFI (Port Fuel Injection) gasoline engines for motorcycles have some problems such as slow transient response because of wall wet of fuel caused by the injector's layout. Hence, it is important to understand the characteristics of fuel sprays such as droplet size and distribution of fuel concentration. Considering the spray formation in a port, there are three kinds of the essential elements: breakup, evaporation and wall impingement. However, it is difficult to observe three of them at the same time. Therefore, the authors have made research step by step. In the authors' previous study, the authors focused on the wall collision, droplet sizes, droplet speeds and the space distribution of the droplets. In this study, the authors focused on evaporation. A direct sampling method using FID (Flame Ionization Detector) for evaporating fuel was established and the concentration distribution of evaporating fuel in the port was measured and analyzed.