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Much effort has been devoted to studies on auto-ignition engines of gasoline including homogeneous-charge combustion ignition engines over 30 years, which will lead to lower exhaust energy loss due to high-compression ratio and less dissipation loss due to throttle-less device. However, the big problem underlying gasoline auto-ignition is knocking phenomenon leading to strong noise and vibration. In order to overcome this problem, we propose the principle of colliding pulsed supermulti-jets. In a prototype engine developed by us, octagonal pulsed supermulti-jets collide and compress the air around the center point of combustion chamber, which leads to a hot spot area far from chamber walls. After generating the hot spot area, the mechanical compression of an asymmetric double piston unit is added in four-stroke operation, which brings auto-ignition of gasoline.

Along with the recent growing concern about global environmental pollution, there has been a movement in automotive engines toward lower fuel consumption, lower emissions, and high output. Accordingly, not only higher ignitability, but also improved performance under severe high temperature conditions are required for spark plugs to follow this trend. To meet these requirements, next-generation high ignitability spark plugs, equipped with an optimized firing end design, have been developed. This paper describes the development of these next-generation high ignitability spark plugs.

The design of spark plugs, critical for igniting the gas mixture in the combustion chamber, must catch up with the latest advances in automotive engine development because many improvements for higher efficiency and lower emissions make combustion more difficult to initiate. Spark plugs must maintain their function in both below freezing environments and high speed, high temperature operation. The performance of a spark plug is characterized by the shape of its firing end exposed in the combustion chamber and the layout of the insulator nose in the metal shell. This paper summarizes recent requirements for spark plugs, proposes a new firing end shape, and evaluates its performance. The relationship between geometric configuration and performance are evaluated on an actual engine. The results demonstrate improved spark plug performance, especially under the most extreme temperature conditions.

In high-swirl engines, such as gas engine, multi-spark discharge causes uneven wear of spark plugs because intense swirl breaks the spark discharge path. The ignition system with variable discharge energy solved this problem. Although the reduced discharge energy may weaken the ignitability, the variable discharge energy keeps high ignitability under any engine operating conditions. Gas engines require higher discharge voltage than gasoline engines. The high required voltage has hindered the development of long-life spark plugs. Attaching sub-electrodes strengthened the electric field intensity and succeeded in lowering the required voltage. The combination of the above-mentioned ignition system and spark plug has extended the plug life span.

There has been strong public demand for reduced hazardous exhaust gas emissions and improved fuel economy for automobile engines. In recent years, a number of innovative solutions that lead to a reduction in fuel consumption rate have been developed, including in-cylinder direct injection and lean burn combustion technologies, as well as an engine utilizing a large volume of exhaust gas recirculation (EGR). Furthermore, a homogeneous charge compression ignition (HCCI) engine is under development for actual application. However, one of the issues common to these technologies is less stable combustion, which causes difficulty in engine management. Additionally, it is now mandatory to provide an onboard diagnosis (OBD) system. This requires manufacturers to develop a technology that allows onboard monitoring and control of the combustion state. This paper reports on an innovative combustion diagnostic method using an in-cylinder pressure sensor.

For the future high power output and low emission engine, the spark plugs need to be improved ignition performance and high thermal resistance with reduced sizes. To accommodate these requirements a new spark plug has been developed with new material and better configurations.

A direct injection system in which fuel was injected through the cylinder wall was developed and detailed investigation was made for the purpose of reducing short-circuit of fuel in 2-stroke engines. As a result of dynamo tests using 430cc single cylinder engine, it was found that the injector was best attached at a location as close to TDC as possible on the rear transfer port side, and that the entire amount of fuel should be injected towards the piston top surface. Emissions were worsened if fuel was injected towards the exhaust port or spark plug. Although the higher injection pressure resulted in large emissions reduction effects, it did not have a significant effect on fuel consumption. When a butterfly exhaust valve, known to be effective against irregular combustion in the light load range, was applied, it was found to lead to further reductions in HC emission and fuel consumption while also improving combustion stability.

To meet the recent emission standard and fuel economy, it is required to scale down engine component sizes. For the ignition system, we would like to reduce the physical size of an ignition coil as well. However the present direct-ignition (DI) engine requires long spark duration time, and which makes difficult to reduce the physical size of the ignition coil. NTK developed a special method to achieve the goal. The presented paper introduces size reduction of the ignition coil and shortening the spark duration time for good ignition performance with the carbon fouling detection capability. Occurrence of the carbon fouling accompanies abnormal spark around the spark nose area always. Accordingly, this paper describes also a method detecting the abnormal spark, by using discharge current method or spark plug voltage. Furthermore, this paper describes the method of early detection of misfire and evasive control by detecting the abnormal spark.

We have attempted to reduce emissions and improve fuel economy of a small utility engine running with a lean A/F ratio under partial load conditions in the most frequent operating mode. However this caused undesirable hunching and many difficulties for running the engine at a lean A/F ratio. We derived the necessary amount of engine speed changes from the relationship between the spark timing and torque to control the hunching by adjusting the spark timing at various engine speeds. The method improved emissions and fuel economy, and made it possible to run the engine smoothly from low engine speed to higher speeds at a high load rating.