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Exhaust gas recirculation (EGR) can be used to mitigate knock in SI engines. However, experiments have shown that the effectiveness of various EGR constituents to suppress knock varies with fuel type and compression ratio (CR). To understand some of the underlying mechanisms by which fuel composition, octane sensitivity (S), and CR affect the knock-mitigation effectiveness of EGR constituents, the current paper presents results from a chemical-kinetics modeling study. The numerical study was conducted with CHEMKIN, imposing experimentally acquired pressure traces on a closed reactor model. Simulated conditions include combinations of three RON-98 (Research Octane Number) fuels with two octane sensitivities and distinctive compositions, three EGR diluents, and two CRs (12:1 and 10:1). The experimental results point to the important role of thermal stratification in the end-gas to smooth peak heat-release rate (HRR) and prevent acoustic noise.

We have developed a novel engine cycle simulation program (UniDES: universal diesel engine simulator) to reproduce the diesel combustion process over a wide range of engine operating parameters, such as the amount of injected fuel, the injection timing, and the EGR ratio. The approach described in this paper employs a zoning model, where the in-cylinder region is divided into up to five zones. We also applied a probability density function (PDF) concept to each zone to consider the effect of spatial non-homogeneities, such as local equivalence ratios and temperature, on the combustion characteristics. We linked this program to the commonly used commercial GT-Power® software (UniDES+GT). As a result, we were able to reproduce transient engine behavior very accurately.

The aim of this research is to develop the diesel combustion simulation (UniDES: Universal Diesel Engine Simulator) that incorporates multiple-injection strategies and in-cylinder composition changes due to exhaust gas recirculation (EGR), and that is capable of high speed calculation. The model is based on a zero-dimensional (0D) cycle simulation, and represents a multiple-injection strategy using a multi-zone model and inhomogeneity using a probability density function (PDF) model. Therefore, the 0D cycle simulation also enables both high accuracy and high speed. This research considers application to actual development. To expand the applicability of the simulation, a model that accurately estimates nozzle sac pressure with various injection quantities and common rail pressures, a model that accounts for the effects of adjacent spray interaction, and a model that considers the NOx reduction phenomenon under high load conditions were added.

Improving vehicle fuel economy is a central part of efforts toward achieving a sustainable society. An effective way for accomplishing this aim is to enhance the engine thermal efficiency. Measures to mitigate knocking and reduce engine cooling heat loss are important aspects of enhancing the engine thermal efficiency. Cooled exhaust gas recirculation (EGR) is regarded as a key technology because it is capable of achieving both of these objectives. For this reason, it has been adopted in a wide range of both hybrid and conventional vehicles in recent years. Toyota has been introducing these technologies as ESTEC (Economy with Superior Thermal Efficient Combustion). Improving cycle-to-cycle variations in combustion, in addition to fast combustion is essential for achieving high engine thermal efficiency.

To correspond to the social requirements such as climate change, air pollution, and energy security, enhancing the engine thermal efficiency is strongly required in these days. As for the specific engine technologies to improve the engine thermal efficiency, Atkinson cycle, cooled EGR (Exhaust Gas Recirculation), and low friction technologies have been developed [1–4]. In regard to combustion technology, lean boosted concept has a potential to reduce CO2 emission because lean boosted concept is expected to enhance the engine thermal efficiency. Although expanding lean combustion limit is important for both increasing the engine thermal efficiency and reducing NOx emission, there is a limitation to realize stable lean combustion with SI (Spark Ignition) gasoline engine. In this study, fuel effects on the combustion characteristics from the viewpoint of chemical reaction capability are focused on.

A new stratified charge combustion system has been developed for direct injection gasoline engines. The special feature of this system is employment of a thin fan-shaped fuel spray formed by a slit nozzle. The stratified mixture is produced by the combination of this fan-spray and a shell-shaped piston cavity. Both under-mixing and over-mixing of fuel in the stratified mixture is reduced by this system. This combustion system does not require distinct charge motion such as tumble or swirl, which enables intake port geometry to be simplified to improve full load performance. The effects of the new system on engine performance at part load are improved fuel consumption and reduced smoke, CO and HC emissions, obviously at medium load and medium engine speed. HC emissions at light load are also improved even with high EGR conditions.

The knock-suppression effectiveness of exhaust-gas recirculation (EGR) can vary between implementations that take EGR gases after the three-way catalyst and those that use pre-catalyst EGR gases. A main difference between pre-and post-catalyst EGR gases is the level of trace species like NO, UHC, CO and H2. To quantify the role of NO, this experiment-based study employs NO-seeding in the intake tract for select combinations of fuel types and compression ratios, using simulated post-catalyst EGR gases as the diluent. The four investigated gasoline fuels share a common RON of 98, but vary in octane sensitivity and composition. To enable probing effects of near-zero NO levels, a skip-firing operating strategy is developed whereby the residual gases, which contain trace species like NO, are purged from the combustion chamber. Overall, the effects of NO-seeding on knock are consistent with the differences in knock limits for preand post-catalyst EGR gases.

The effects of blending ETBE to diesel fuel on the characteristics of low temperature diesel combustion and exhaust emissions were investigated in a naturally-aspirated DI diesel engine with large rates of cooled EGR. Low temperature smokeless diesel combustion in a wide EGR range was established with ETBE blended diesel fuel as mixture homogeneity is promoted with increased premixed duration due to decreases in ignitability as well as with improvement in fuel vaporization due to the lower boiling point of ETBE. Increasing the ETBE content in the fuel helps to suppress smoke emissions and maintain efficient smokeless operation when increasing EGR, however a too high ETBE content causes misfiring at larger rates of EGR. While the NOx emissions increase with increases in ETBE content at high intake oxygen concentrations, NOx almost completely disappears when reducing the intake oxygen content below 14 % with cooled EGR.

The dynamics model and model-based controller (LQG servo controller) have been constructed to improve performance of diesel engine in transient condition. The input parameters of the model are fuel quantity of main injection, timing of main injection, fuel quantity of pilot injection, timing of pilot injection, external EGR ratio and boost pressure. The parameters that are succeeded between cycles to express transient condition are residual gas temperature and of residual oxygen. In the model, one cycle is discretized into 10 representative points. The precision of the accuracy of the model and the responsiveness of the controller were confirmed.

To correspond to the social requirements such as energy security, and climate change, enhancing engine thermal efficiency is strongly required in these days. As for the specific engine technologies to improve engine thermal efficiency, Atkinson cycle, cooled EGR (Exhaust Gas Recirculation), and low friction technologies have been developed [1, 2, 3, 4]. As a result, the current maximum thermal efficiency comes close to 40%. However, since it is considered that much higher engine thermal efficiency is required in the future to meet more stringent social requirements, a new prototype L4 engine which features a long stroke design with a high tumble is investigated to clarify the future direction in this paper. In regard to combustion, the lean boosted concept with cooled EGR is examined. In consequence, it is shown that more than 45% engine thermal efficiency can be achieved. This paper describes the means to enhance engine thermal efficiency and a future possibility.

The effects of an increasing boost pressure, a high EGR rate and a high injection pressure on exhaust emissions from an HSDI (High Speed Direct Injection) diesel engine were examined. The mechanisms were then investigated with both in-cylinder observations and 3DCFD coupled with ϕT-map analysis. Under a high-load condition, increasing the charging efficiency combined with a high injection pressure and a high EGR rate is an effective way to reduce NOx and soot simultaneously, which realized an ultra low NOx of 16ppm at 1.7MPa of IMEP (Indicated Mean Effective Pressure). The flame temperature with low NOx and low soot emissions is decreased by 260K from that with conventional emissions. Also, the distribution of the fuel-air mixture plot on a ϕT-map is moved away from the NOx and soot formation peninsula, compared to the conventional emissions case.

Effects of fuel distillation characteristics and cetane number on premixed charge compression ignition (PCCI) combustion were investigated for the purpose of reducing NOx and PM emissions from a direct injection diesel engine. The test engine had a hole type injection nozzle for conventional diesel combustion at high load operation. A low compression ratio and cooled EGR were applied to the test engine in order to reduce the compression temperature for avoiding pre-ignition. The investigation results show that, in the case of ignition control by EGR, a light fuel with lower distillation characteristics had an advantage of reducing smoke at higher loads. This means that high volatility fuel is effective in promoting lean mixture formation of fuel and air during the ignition delay. Moreover, lowering the cetane number was effective in reducing NOx emissions by suppression of combustion temperature.

A concept of dual-fuel, Premixed Compression Ignition (PCI) combustion controlled by two fuels with different ignitability has been developed to achieve drastically low NOx and smoke emissions. In this system, isooctane, which was used to represent high-octane gasoline, was supplied from an intake port and diesel fuel was injected directly into an engine cylinder at early timing as ignition trigger. It was found that the ignition timing of this PCI combustion can be controlled by changing the ratio of amounts of injected two fuels and combustion proceeds very mildly by making spatial stratifications of ignitability in the cylinder even without EGR, as preventing the whole mixture from igniting simultaneously. The operable range of load, where NOx and smoke were less than 10ppm and 0.1 FSN, respectively, was extended up to 1.2MPa of IMEP using an intake air boosting system together with dual fueling.

The emissions reduction potential of neat GTL (Gas to Liquids: Fischer-Tropsch synthetic gas-oil derived from natural gas) fuels has been preliminarily evaluated by three different latest-generation diesel engines with different displacements. In addition, differences in combustion phenomena between the GTL fuels and baseline diesel fuel have been observed by means of a single cylinder engine with optical access. From these findings, one of the engines has been modified to improve both exhaust emissions and fuel consumption simultaneously, assuming the use of neat GTL fuels. The conversion efficiency of the NOx (oxides of nitrogen) reduction catalyst has also been improved.

Reflecting on the world's trend on saving crude oil consumption and to create an economical fuel efficient vehicle for the increasing world population, a new THS-II HV powertrain has been developed for the compact vehicle class. The application of a THS type powertrain for the compact vehicle class was a first for the world and to achieve it, brand new hardware, and software needed to be developed. For the Internal Combustion Engine (ICE), state of the art technologies such as the use of the Atkinson cycle with Variable Valve Timing (VVT), cooled exhaust gas recirculation (EGR), an electric water pump, a compact exhaust manifold, a Low Friction chain, beltless system and exhaust heat recovery system were applied. For the electric motor, copper wire with a rectangular cross section and divided stator cores combined with a newly developed production process were applied for higher volumetric density.

A new V-6 stoichiometric gasoline direct injection engine was developed for high performance FR (Front Engine Rear Drive) vehicles. High power performance, low fuel consumption and low exhaust emissions were achieved by employing a stoichiometric direct injection system that uses Toyota's unique slit nozzle injector that generates a fan-shaped fuel spray and variable intake and exhaust valve timing systems. Focusing on the power performance, maximum power of 183kW (61kW/L) is achieved at 6200rpm and maximum torque is 312Nm at 3600rpm. This power performance is among the top production 3.0 L gasoline engines in the world. This paper outlines the features of this engine and some special technologies contributing to the achievement of the above-mentioned high performance. Optimizing the intake-port design was done to improve power performance.

In recent years, attention has been focused on a hybrid vehicle capable of substantial reductions in CO2 exhaust emissions. This paper describes the newly developed 1.8-liter 2ZR-FXE gasoline engine for use with a hybrid system for compact vehicles, which effectively combines higher driving performance with higher fuel efficiency. This engine was based on the 1.8-liter 2ZR-FE engine with outstanding performance and fuel efficiency. This engine has achieved high thermal efficiency by using the high-expansion ratio cycle “Atkinson cycle”, as with the previous 1NZ-FXE engine. Additionally, a new cooled Exhaust Gas Recirculation (EGR) system and electric water pump were adopted to further improve fuel efficiency. A high efficiency cooler was used to cool the EGR gas, which enabled the introduction of the EGR gas at high load conditions, and exhaust gas temperature was reduced.

Low pressure loop (LPL) EGR systems are effective means of simultaneously reducing the NOx emissions and fuel consumption of diesel engines. Further lower emission levels can be achieved by adopting a system that combines LPL EGR with a NOx storage and reduction (NSR) catalyst. However, this combined system has to overcome the issue of combustion fluctuations resulting from changes in the air-fuel ratio due to EGR gas recirculation from either NOx reduction control or diesel particulate filter (DPF) regeneration. The aim of this research was to reduce combustion fluctuations by developing LPL EGR control logic. In order to control the combustion fluctuations caused by LPL EGR, it is necessary to estimate the recirculation time. First, recirculation delay was investigated. It was found that recirculation delay becomes longer when the LPL EGR flow rate or engine speed is low.

Improving vehicle fuel economy is a central part of efforts toward achieving a sustainable society. An effective way of accomplishing this is to enhance the engine thermal efficiency. Mitigating knock and reducing engine heat loss are important aspects of enhancing the thermal efficiency. Cooled exhaust gas recirculation (EGR) is regarded as a key technology because it is capable of achieving both of these objectives. For this reason, it has been adopted in a wide range of both hybrid vehicles and conventional vehicles in recent years. In EGR equipped engines, fast combustion is regarded as one of the most important technologies, since it realizes higher EGR ratio. To create fast combustion, generation of strong in-cylinder turbulence is necessary. Strong in-cylinder turbulence is achieved through swirl, squish, and tumble flows. Specifically high tumble flow has been adopted on a number of new engines because of the intense effect of promoting in-cylinder turbulence.

Due to regulations for even lower levels of pollutants in exhaust gas, development of advanced combustion techniques and increasingly efficient catalysts has become more crucial than ever. One of the essential technologies to achieve this goal is an advanced measurement method, which can detect the characteristics of exhaust gas, such as temperature and chemical compositions, in real-time to clarify their reaction mechanisms. A direct and fast response (1ms) measurement technique was developed based on diode laser absorption spectroscopy and applied to practical engine exhaust measurement to prove the validity of this technology for various applications such as clarification of engine start phenomena and improvement of EGR controls.