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In recent years, improvements in the fuel economy and exhaust emission performance of internal combustion engines have been increasingly required by regulatory agencies. One of the salient concerns regarding general purpose engines is the larger amount of CO emissions with which they are associated, compared with CO emissions from automobile engines. To reduce CO and other exhaust emissions while maintaining high fuel efficiency, the optimization of total engine system, including various design parameters, is essential. In the engine system optimization process, cycle simulation using 0-D and 1-D engine models are highly useful. To define an optimum design, the model used for the cycle simulation must be capable of predicting the effects of various parameters on the engine performance. In this study, a model for predicting the performance of a general purpose SI (Spark Ignited) engine is developed based on the commercially available engine simulation software, GT-POWER.

The introduction of real driving emissions cycles and increasingly restrictive emissions regulations force the automotive industry to develop new and more efficient solutions for emission reductions. In particular, the cold start and catalyst heating conditions are crucial for modern cars because is when most of the emissions are produced. One interesting strategy to reduce the time required for catalyst heating is post-oxidation. It consists in operating the engine with a rich in-cylinder mixture and completing the oxidation of fuel inside the exhaust manifold. The result is an increase in temperature and enthalpy of the gases in the exhaust, therefore heating the three-way-catalyst. The following investigation focuses on the implementation of post-oxidation by means of scavenging in a four-cylinder, turbocharged, direct injection spark ignition engine. The investigation is based on detailed measurements that are carried out at the test-bench.

To avoid knocking phenomena, a special crank mechanism for gasoline engine that allowed the piston to move rapidly near TDC (Top Dead Center) was developed and experimentally demonstrated in the previous study. As a result, knocking was successfully mitigated and indicated thermal efficiency was improved [1],[2],[3],[4]. However, performance of the proposed system was evaluated at only limited operating conditions. In the present study, to investigate the effect of piston movement near TDC on combustion characteristics and indicated thermal efficiency and to clarify the knock mitigation mechanism of the proposed method, experimental studies were carried out using a single cylinder engine with a compression ratio of 13.7 at various engine speeds and loads. The special crank mechanism, which allows piston to move rapidly near TDC developed in the previous study, was applied to the test engine with some modification of tooling accuracy.

The authors investigated the reasons of how a preignition occurs in a highly boosted gasoline engine. Based on the authors' experimental results, theoretical investigations on the processes of how a particle of oil or solid comes out into the cylinder and how a preignition occurs from the particle. As a result, many factors, such as the in-cylinder temperature, the pressure, the equivalence ratio and the component of additives in the lubricating oil were found to affect the processes. Especially, CaCO3 included in an oil as an additive may be changed to CaO by heating during the expansion and exhaust strokes. Thereafter, CaO will be converted into CaCO3 again by absorbing CO2 during the intake and compression strokes. As this change is an exothermic reaction, the temperature of CaCO3 particle increases over 1000K of the chemical equilibrium temperature determined by the CO2 partial pressure.

A model combustion chamber of Wankel type rotary engine was employed to study the DISC RE system. A two-stroke Diesel engine's cylinder head was replaced with this combustion chamber to simulate temporal change of air flow and pressure fields inside the chamber as an actual engine. The base engine was motorized to operate as a continuous rapid compression and expansion machine. Pilot fuel spray was injected onto a glow plug to form a pilot flame and it ignites the main fuel spray. The ignitability of pilot fuel, mixture formation process, ignition process of main fuel by pilot flame and the effect of pilot and main injection timings on combustion characteristics were examined.

A new combustion method of high compression ratio SI engine was studied and proposed in order to achieve higher thermal efficiency of SI engine comparable to that of CI engine. Compression ratio of SI engine is generally restricted by the knocking phenomena. A combustion chamber profile and a cranking mechanism are studied to avoid knocking with high compression ratio. Since reducing the end-gas temperature will suppress knocking, a combustion chamber was considered to have a wide surface at the end-gas region. However, wide surface will lead to high heat loss, which may cancel the gain of higher compression ratio operation. Thereby, a special cranking mechanism was adopted which allowed the piston to move rapidly near TDC. Numerical simulations were performed to optimize the cranking mechanism for achieving higher thermal efficiency. An elliptic gear system and a leaf-shape gear system were employed in the simulations.

The objective of this study is to extend the high load operation limit of a gasoline HCCI engine. A new system extending the high load HCCI operation limit was proposed, and the performance of the system was experimentally demonstrated. The proposed system consists of two new techniques. The first one is the “Blow-down super charging (BDSC) system”, in which, EGR gas can be super charged into a cylinder during the early stage of compression stroke by using the exhaust blow-down pressure wave from another cylinder phased 360 degrees later/earlier in the firing order. The other one is “EGR guide” for generating a large thermal stratification inside the cylinder to reduce the rate of in-cylinder pressure rise (dP/dθ) at high load HCCI operation. The EGR guides consist of a half-circular part attached on the edge of the exhaust ports and the piston head which has a protuberant surface to control the mixing between hot EGR gas and intake air-fuel mixture.

In recent years, the improvement in the fuel efficiency and reduction in CO2 emission from internal combustion engines has been an urgent issue. The lean burn technology is one of the key technologies to improve thermal efficiency of SI engines. However, combustion stability deteriorates at lean burn operations. The reduction in cycle-to-cycle and cylinder-to-cylinder variations is one of the major issues to adapt the lean burn technique for production engines. However, the details of the causes and mechanisms for the combustion variations under the lean burn operations have not been cleared yet. The purpose of this study is to control cylinder to cylinder combustion variation. A conventional turbocharged direct injection SI engine was used as the test engine to investigate the effect of engine control parameters on the cylinder to cylinder variations. The engine speed is set at 2200 rpm and the intake pressure is set at 58, 78, 98 kPa respectively.

In order to enhance the reliability of a pilot flame ignition system, three kinds of subchambers in which a pilot injector and a glow plug were set up were tested with a model combustion chamber of DISC rotary engine. A two-stroke Diesel engine's cylinder head was replaced with this model combustion chamber to simulate temporal changes of air flow and pressure fields inside the chamber as an actual engine. The behavior of the pilot flame generated in the subchamber, ignition process of main fuel spray by the pilot flame, the most suitable mixture distribution between the main chamber and the subchamber, and the effect of nozzle diameter of main injector on combustion characteristics were studied by using a high-speed video camera and ion probes.

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.

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.

A swirl-type injector is commonly used for the gasoline direct injection IC engines. To control and optimize the engine combustion, analyses of mixture formation process inside the cylinder are quite important. In this study, an evaluation of a DDM (Discrete Droplet Model) including breakup and evaporation sub-models has been made by making comparisons between the calculation and measurement. In the calculation, two kinds of initial conditions were tested; one was from empirical expressions and the other was from calculated results using a VOF (Volume Of Fluid) model that had a feature to examine the free fluid surface of a liquid fuel spray. As a result, the authors have found that a DDM can basically explain the spray formation process. However, much further modification of the breakup model and initial conditions would be required to have a quantitatively good agreement between the calculation and measurement

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.

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.

In order to extend the HCCI high load operational limit, the effects of the distributions of temperature and fuel concentration on pressure rise rate (dP/dθ) were investigated through theoretical and experimental methods. The Blow-Down Super Charge (BDSC) and the EGR guide parts are employed simultaneously to enhance thermal stratification inside the cylinder. And also, to control the distribution of fuel concentration, direct fuel injection system was used. As a first step, the effect of spatial temperature distribution on maximum pressure rise rate (dP/dθmax) was investigated. The influence of the EGR guide parts on the temperature distribution was investigated using 3-D numerical simulation. Simulation results showed that the temperature difference between high temperature zone and low temperature zone increased by using EGR guide parts together with the BDSC system.

In internal combustion engine development, the ongoing research can be mainly classified into two categories based on the purpose: limiting exhaust emissions and searching for alternative fuels. One of the effective approaches reduce emissions is the improvement of thermal efficiency. Certain types of alternative fuels derived from renewable resources were estimated to confirm the thermal efficiency. This study uses a single-cylinder engine added with olefin and oxygenated additive fuel, such as 1-hexene, ethanol, and ETBE, to evaluate the parameters that affect thermal efficiency. Furthermore, the effects of various additive fuels are summarized and essential information is provided for determining next- generation fuel composition.

In reciprocating internal combustion engines, the Otto cycle indicates the best thermal efficiency under a given compression ratio. To achieve an ideal Otto cycle, combustion must take place instantaneously at top dead center, but in fact, this is impossible. Meanwhile, if we allow slower piston motion around top dead center, combustion will be promoted at that period; then both the in-cylinder pressure and degree of constant volume will increase, leading to higher thermal efficiency. In order to verify this hypothesis, an engine with slower piston motion around top dead center, using an ideal constant volume combustion engine, was built and tested. As anticipated, the degree of constant volume increased. However, thermal efficiency was not improved, due to increased heat loss.

Effects of measurement method, coolant temperature and fuel composition on soot emissions were examined by engine experiments. By reducing the pressure fluctuation in the sampling line, the measured soot emissions with better stability and reproducibility could be obtained. With lower coolant temperatures, larger soot emissions were yielded at much advanced fuel injection timings. Compared to gasoline, soot emissions with a blend fuel of normal heptane, isooctane and toluene were significantly decreased, suggesting the amounts of aromatic components (toluene or others) should be increased to obtain a representative fuel for the predictive model of particulate matter in SIDI engines.

The stochastic pre-ignition phenomenon plays a vital role to limit the further increasing BMEP for natural gas engines. In this study, the pre-ignition propensities were examined in a highly boosted premixed natural gas engine by various engine loads and air/fuel ratios, as well as different methane number (MN) altered by hydrogen addition. A proper pre-ignition evaluation method was proposed referring to intake temperature. Moreover, the limits of in-cylinder temperature and pressure for the onset of pre-ignition were estimated. The results show that both higher IMEP and richer mixture conditions readily lead to pre-ignition. The significant increases of pre-ignition frequency and heavy-knocking pre-ignition cycle present with lowering MN.

HCCI combustion can realize low NOx and particulate emissions and high thermal efficiency. Therefore, HCCI combustion has a possibility of many kinds of applications, such as an automotive powertrain, general-purpose engine, motorcycle engine and electric generator. However, the operational range using HCCI combustion in terms of speed and load is restricted because the onset of ignition and the heat release rate cannot be controlled directly. For the extension of the operational range using either an external supercharger or a turbocharger is promising. The objective of this research is to investigate the effect of the intake pressure on the HCCI high load limit and HCCI combustion characteristics with blowdown supercharging (BDSC) system. The intake pressure (Pin) and temperature (Tin) were varied as experimental parameters. The intake pressure was swept from 100 kPa (naturally aspirated) to 200 kPa using an external mechanical supercharger.