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Spray-guided gasoline direct injection SI engines attract as one of new generation lean-burn engines to promise CO2 reduction. These typically adopt “narrow-spacing” concept in which an injector is centrally mounted close to a spark plug. Therefore, geometric targets of the fuel spray and a position of the spark plug have to be exactly limited to maintain a proper mixture in the spark gap. In addition, the stable combustion window is narrow because the spark ignition is limited in a short time during and immediately after the injection. These spatial and temporal restrictions involve some intractable problems concerning the combustion robustness due to the complicate phenomena around the spark plug. The local mixture preparation near the spark plug significantly depends on the spray-induced charge motion. The intense flow induced by the motion blows out and stretches the spark, thereby affecting the spark discharge performance.

A fuel control method to reduce the harmful exhaust gas from SI engines is proposed. As is well known, both the amplitude and the frequency of the limit cycle in a conventional air-fuel ratio control system are determined uniquely by parameters in the system. And this limits our making full use of the oxygen storage effect of TWC. A simple model of TWC reaction revealed the relationship between maximum conversion efficiency and both the amplitude and the frequency in a air fuel control system. It also revealed that TWC conversion efficiency attained to maximum levels when both the amplitude and the frequency of the limit cycle are selected so as to make full use of the oxygen storage effect of TWC. In order to achieve this, it is necessary to vary both the amplitude and the frequency arbitrarily.

A flexible fuel vehicle (FFV) was evaluated through various tests for its potential as an alternative to the conventional gasoline vehicle. This paper presents the systems incorporated in the FFV and the test results. 50,000 mile emission durability tests were also performed and the potential of the FFV as a “Low Emission Vehicle” was assessed. As the result of extensive engineering work, we successfully developed a Galant FFV which exhibits very good durability and reliability. The emission control system which we have developed demonstrated that the vehicle has a good potential to comply with the California formaldehyde emission standard of 15 mg/mile. However, due to the large portion of unburnt methanol in the tail-pipe emissions, FFVs will have more difficulty than gasoline vehicles in meeting non-methane organic gas (NMOG) standards applicable to “Low Emission Vehicles”.

GDI (Gasoline Direct Injection) engine adopting new combustion control technologies was developed and introduced into Japanese domestic market in August of 1996. In order to extend its application to the European market, various system modifications have been performed. Injectors are located with a smaller angle to the vertical line in order to improve the combustion stability in the higher speed range. A new combustion control method named “two-stage mixing” is adopted to suppress the knock in the low speed range. As a result of this new method, the compression ratio was increased up to 12.5 to 1 while increasing the low-end torque significantly. Taking the high sulfur gasoline in the European market into account, a selective reduction lean-NOx catalyst with improved NOx conversion efficiency was employed. A warm-up catalyst can not be used because the selective reduction lean NOx catalyst requires HC for the NOx reduction.

Spray motion visualization, mixture strength measurement, flame spectral analyses and flame behavior observation were performed in order to elucidate the mixture preparation and the combustion processes in Mitsubishi GDI engine. The effects of in-cylinder flow called reverse tumble on the charge stratification were clarified. It preserves the mixture inside the spherical piston cavity, and extends the optimum injection timing range. Mixture strength at the spark plug and at the spark timing can be controlled by changing the injection timing. It was concluded that reverse tumble plays a significant role for extending the freedom of mixing. The characteristics of the stratified charge combustion were clarified through the flame radiation analyses. A first flame front with UV luminescence propagates rapidly and covers all over the combustion chamber at the early stage of combustion.

With the intention of improving engine performance and emissions, the authors examined the influence of the method of initial fuel injection quantity reduction and of the injector configuration of a common rail fuel injection system on engine performance and exhaust emissions. Results showed that decreasing the nozzle hole diameter was an effective way to reduce the initial injection quantity without increasing black smoke. Compared to a three-way type injector, it was found that a two-way type injector can greatly reduce the amount of fuel leakage from the electromagnetic injector control valve and fuel consumption could be further improved by reduction of the driving loss. Furthermore, the increase of driving losses with higher injection pressure was small, and as a result, higher pressure injection was possible.

The 4M5 series of four-cylinder, in-line, direct-injection diesel engines has been released by Mitsubishi Motors Corporation for light and medium-duty trucks and buses. Featuring an updated structure and reflecting the employment of state-of-the-art technology in the design of every component, the new engine series offers high reliability and compact dimensions. Moreover, the new series well meets contemporary demands for high performance, low noise, and clean combustion.

Injection rate control is an important capability of the ideal injection system of the future. However, in a conventional Common-Rail System (CRS) the injection pressure is constant throughout the injection period, resulting in a nearly rectangular injection rate shape and offering no control of the injection rate. Thus, in order to realize injection rate control with a CRS, a "Next- generation Common-Rail System (NCRS)" was conceptualized, designed, and fabricated. The NCRS has two common rails, for low- and high-pressure fuel, and switches the fuel pressure supplied to the injector from the low- to the high- pressure rail during the injection period, resulting in control over the injection rate shape. The effects of injection rate shape on exhaust emissions and fuel consumption were investigated by applying this NCRS to a single- cylinder research engine.

The gasoline direct injection engine starts significantly faster than a conventional engine. Fuel can be injected into the cylinder during the compression stroke at the same time of cranking start. When the spark plug ignites the mixture at the end of compression stroke, the engine has its first combustion, that is, the first combustion occurs within 0.2 sec after the start of cranking. This unique characteristic of quick startability has realized a idle stop system, which enables drivers to operate the vehicle in a natural manner.

A two-stage combustion is one of the Mitsubishi GDI™ technologies for a quick catalyst warm-up on a cold-start. However, when the combustion is continued for a long time, an increase in the fuel consumption is a considerable problem. To solve the problem, a stratified slight-lean combustion is newly introduced for utilization of catalysis. The stratified mixture with slightly lean overall air-fuel ratio is prepared by the late stage injection during the compression stroke. By optimizing an interval between the injection and the spark timing, the combustion simultaneously supplies substantial CO and surplus O2 to a catalyst while avoiding the soot generation and the fouling of a spark plug. The CO oxidation on the catalyst is utilized to reduce the cold-start emissions. Immediately after the cold-start, the catalyst is preheated for the minimum time to start the CO oxidation by using the two-stage combustion. Following that, the stratified slight-lean combustion is performed.

The need of lightweight vehicle design is motivated by the recent global trend of less fuel consumption and lower emission in vehicle. However in NVH development of vehicle, it becomes more difficult for the lightweight vehicle to reach low vibro-acoustic sensitivity than, for the heavy weight one to do so. Inthis environment, this paper describes about the practical finite element (FE) modeling of vehicle structure and acoustics, in order to predict "boom" response to powertrain excitation. The FE modeling process through validation and updating with experimental mode makes, the accumulation of considerable expertise for improving prediction accuracy, possible. FE analysis based on this modeling process is so useful for predicting "boom" levels up to 200 Hz. Using the result of FE analysis, structural optimization is executed in order to improve "boom" level of 80 Hz.

As the global environmental protection becomes the world consensus recently, the regulations of the fuel consumption and the exhaust gas have large effects on the performance and the fundamental structure of commercial vehicles. Especially the technology concerning "fluid" and "heat" has a close relationship with those issues. Owing to above circumstances, commercial vehicles such as large trucks and buses are forced to be designed near the limit of allowance. Furthermore, a rapid design is another requirement. However, though significant number of variations, i.e., cab configuration, wheel base, rear body configuration, engine specification, etc., are prepared, it is impossible to improve the performance of all those combinations by experiments which cost a lot. Accordingly, the quantitative prediction using computer will become indispensable at the beginning term of new car development.

A characteristic mechanism of in-cylinder combustion is “time-domain mixing” which mixes up unburned gas, products in the different stages of combustion process, and burned gas, by “eddy”, a flow component with its scales of several to 10 mm. It seems to play a role in completing the combustion. Now that direct injection is a central engine technology, a keyword to combustion control is “freedom of mixing”, that is, no restriction on mixture formation, realized by direct injection. Various kinds of combustion control technologies utilizing it, have been presented. After combustion control for a premixed leanburn gasoline engine, and a direct injection gasoline engine, was achieved by turbulence control, and mixing control, respectively, the next target of combustion control will be ignition control. It will be possible, by controlling some boundary condition on combustion and fuel chemistry. Time-domain mixing and freedom of mixing will support it.

Two-stage hybrid combustion for a 6-stroke gasoline direct injection SI engine is a new strategy to control the ignition of the HCCI combustion using hot-burned gas from the stratified lean SI combustion. This combustion is achieved by changing the camshafts, the cam-driven gear ratio and the engine control of a conventional 4-stroke gasoline direct injection engine without using a higher compression ratio, any fuel additives and induction air heating devices. The combustion processes are performed twice in one cycle. After the gas exchange process, the stratified ultra-lean SI combustion is performed. The hot-burned gas generated from this SI combustion is used as a trigger for the next HCCI combustion. After gasoline is injected in the burned gas, the hot and homogeneous lean mixture is recompressed without opening the exhaust valves. Thus the HCCI combustion occurs.

A stratified-charge lean-burn engine is newly developed for the purpose of energy saving and carbon dioxide reduction to minimize the global warming. The engine, named MVV(Mitsubishi Vertical Vortex)engine, is based on the unique vertical vortex technology which realizes stable combustion even with lean mixture without any additional device. And it also has another feature of “all range air-to-fuel ratio feedback control system” utilizing linear air-to-fuel ratio sensor. This paper describes various technologies developed in this engine.

A novel leanburn concept, ‘Barrel-Stratification’ is proposed. Fuel is introduced into the cylinder through one of the intake ports of a dual-intake-valve engine of which the tumbling air motion is intensified by the sophisticated intake port design. Because the velocity component in the direction parallel to the axis of tumble is small, charge stratification realized during the intake stroke is maintained until the end of the compression stroke. By the effects of charge stratification and the turbulence enhancement by tumble, stable combustion is realized even at extremely lean conditions. The concept was verified by flow field analysis applying a multi-color laser sheet technique and the flame structure analysis employing the blue-end image intensification realized by the interference mirror and the short delay phosphor.

In the heavy-duty commercial vehicle market in Japan, particularly in the segment of dump trucks and tractors, naturally aspirated engines maintain a dominant market share because of their superior torque characteristics in the low speed range. In order to meet the ever increasing needs for higher speeds of transportation, better fuel economy and higher reliability, and the needs for increasingly strict exhaust emission regulations, Mitsubishi Motors Corporation (MMC) has developed the 8M20, a 20 liter V8 diesel engine. The '92 model series of “THE GREAT”, MMC's main heavy-duty trucks, has featured this new and powerful engine and has been in the market place since October, 1991. The 8M20 is a naturally aspirated engine that provides an output of 294kW/2200rpm, complying with the current Japanese exhaust emission regulations.

To reduce friction is required to improve engine fuel economy. This study aimed to reduce piston skirt friction, which is a major factor in engine friction. ‘Soft skirt’ is a trendy item in recent gasoline engines, which can improve skirt sliding condition by larger deformation when the piston is pressed to the liner. The effect is confirmed by friction measurement and oil film observation, using prototype pistons. And also one major factor of the effect is clarified that not only side force but also cylinder pressure causes effective deformation of the skirt to create thick oil film at early combustion stroke.

In order to reduce exhaust emission and combustion noise and to improve fuel consumption, the effects of the combustion system parameters of a diesel engine, such as injection pressure, injection nozzle hole diameter, swirl ratio, and EGR rate on exhaust emissions, combustion noise and fuel consumption are investigated and described in detail by analyzing rate of heat release, needle valve lift and injection pressure. Based on these results, reduction of exhaust emission and combustion noise and improvement of fuel consumption are described in the latter part of this paper. These results are shown as follows. The smaller nozzle hole diameter is effective for reducing smoke and PM, and by optimizing the injection timing and swirl ratio, NOx can also be reduced. In addition to the above, by applying EGR and higher injection pressure it is possible to improve the fuel consumption with the remaining low NOx and PM.

Flow and flame structure visualization and modeling were performed to clarify the characteristics of bulk flow, turbulence and mixing in a four-valve engine to adopt the lean combustion concept named “Barrel-Stratification” to the larger displacement center-spark four-valve engine. It was found that the partitions provided in the intake port and the tumble-control piston with a curved-top configuration were effective to enhance the lean combustion of such an engine. By these methods, the fuel distribution in the intake port and the in-cylinder bulk flow structure are optimized, so that the relatively rich mixture zone is arranged around the spark plug. The tumble-control piston also contributes to optimize the flow field structure after the distortion of tumble and to enable stable lean combustion.