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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.

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.

The use of exhaust gas recirculation (EGR) in spark ignition engines has been shown to have a number of beneficial effects under specific operating conditions. These include reducing pumping work under part load conditions, reducing NOx emissions and heat losses by lowering peak combustion temperatures, and by reducing the tendency for engine knock (caused by end-gas autoignition) under certain operating regimes. In this study, the effects of EGR addition on knocking combustion are investigated through a combined experimental and modeling approach. The problem is investigated by considering the effects of individual EGR constituents, such as CO2, N2, and H2O, on knock, both individually and combined, and with and without traces species, such as unburned hydrocarbons and NOx. The effects of engine compression ratio and fuel composition on the effectiveness of knock suppression with EGR addition were also investigated.

Closed-loop robust control system that can monitor combustion state and control it into optimal state using crank angular velocity analysis was established. The system can be constructed without any change of the current hardware. It can avoid engine stall, deterioration of drivability and white smoke emission by misfire after filling low cetane fuels. This study was attempted to grasp the frequency characteristics of crank angular velocity both normal combustion and misfire with FFT (Fast Fourier Transform) and Wavelet Transform. FFT used for frequency analysis is generic method to acquire the frequency characteristics of steady oscillation, however is unsuitable for acquiring the frequency characteristics of transient oscillation. Therefore authors adopted Wavelet Transform and succeeded in grasping the phenomenon in misfiring in time sequential.

In this study, we combined a diesel engine with the Toyota Hybrid System (THS). Utilizing the functions of the THS, reducing engine friction, lowering the compression ratio, and adopting a low pressure loop exhaust gas recirculation system (LPL-EGR) were examined to achieve both low fuel consumption and low nitrogen oxides (NOx) emissions over a wide operating range. After applying this system to a test vehicle it was verified that the fuel economy greatly surpassed that of a conventional diesel engine vehicle and that NOx emissions could be reduced below the value specified in the Euro 6 regulations without DeNOx catalysts.

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.

Numerical 3-D simulations are performed for the improvement of the new direct injection gasoline engine. A solution based local grid refinement method has been developed in order to reduce the CPU time. This method has been incorporated into the CFD program (STAR-CD) with in-house spray and combustion models. Calculation results were compared with the experimental data taken by the LIF technique, and good agreement was obtained for the mixture formation and combustion processes. Some calculations were carried out for the fuel-air mixture formation process during late injection stratified combustion and the following results were obtained. The unburnt fuel has a tendency to remain in the side of the piston cavity at the latter part of the combustion period. To reduce the amount of unburnt fuel, it was shown that the combination of a thin thickness fan spray and compact cavity forms a spherical mixture, suitable for combustion.

A direct injection (DI) gasoline engine having a new stratified charge combustion system has been developed. This new combustion process (NCP) was achieved by a fan-shaped fuel spray and a combustion chamber with a shell-shaped cavity in the piston. Compared with the current Toyota D-4 engine, wider engine operating area with stratified combustion and higher output performance were obtained without a swirl control valve (SCV) and a helical port. This report presents the results of combustion analyses to optimize fuel spray characteristics and piston cavity shapes. Two factors were found to be important for achieving stable stratified combustion. The first is to create a ball-shaped uniform mixture cloud in the vicinity of the spark plug. The optimum ball-shaped mixture cloud is produced with a fuel spray having early breakup characteristics and uniform distribution, and a suitable side wall shape in the piston cavity to avoid the dispersion of the mixture.

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.

Effects of spray characteristics for stratified combustion of direct injection gasoline engine have been researched. The highly functional piezoelectric (PZT) injector was selected for this research. A hole and swirl nozzle were examined in a wide range of fuel pressure. The hole nozzle aims to make stratified mixture formation by vaporizing fuel on the piston, and the swirl nozzle aims to do so in the air above the piston by utilizing the spray characteristic of lower penetration and higher dispersibility. Both sprays could realize stable stratified combustion. The stability mainly depends on the combination of spray characteristic and piston cavity shape, and the swirl air motion which strength changes corresponding to engine operating conditions. The hole nozzle requires high, and the swirl nozzle less fuel pressure. Even by a large amount of EGR, stratified combustion has the advantage of combustion stability, and is useful to reduce exhaust emissions, especially NOx emissions.

A two-color high speed shutter TV camera system has been developed as a new sensing device for measuring the flame temperature in engines. The TV camera system can measure the radiant intensities of high temperature substances accurately and rapidly. And, the two-dimensional temperature distribution can be easily calculated from the radiant intensities by using an image processor. This system is applicable to measurement of flame temperatures in diesel and gasoline engines. The relation between the progress of combustion phenomena and the measured temperature distribution is clearly explained. It is confirmed that the system is effective for measurement of the flame temperature distribution in engines.

An ultra-high speed shutter TV camera including an image intensifier which has a light magnification of 20,000, and an image analysis system have been developed and applied to knock research with a transparent piston engine. Irregularity in the flame configuration was observed just when the pressure vibration began. The causes of cycle to cycle variation of knock intesity were examined through the simultaneous recording of the pressure vibration and the image of the flame.

A television viewing system with a high speed shutter TV camera has been developed for viewing and recording combustion processes in internal combustion engines. The technique has been applied to the study of combustion events in an engine with a transparent piston. The recorded combustion images were analyzed and statistically processed by a microcomputer for summation, averaging, and contour forming. The averaged flame propagation patterns are discussed in comparison with the gas flow motion and cylinder pressure data obtained by conventional methods. This TV technique is easy and effective in obtaining combustion data for various operating conditions and engine geometries.