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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.

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.

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.

The durability of a piston is an essential factor that limits the engine performance. The temperature of a piston, therefore, is valuable information for the development of an engine. As the conventionally applied material hardness method is not a direct measurement of temperature during operation, this method is useful only under constant-speed operating conditions and unable to satisfy various demands of piston temperature measurement. The authors have, therefore, developed the piston temperature measurement system that withstands high engine speed using the compact and light-weight electromagnetic induction method that permits direct measurements of piston temperatures with a thermistor and allows measurement information exchange near the bottom dead center. The system is applicable to motorcycle engines which often use high speed allows measurement up to 15,300 r/min and assures durability and reliability for more than 10 hours.

In order to improve thermal efficiency of spark ignition engines, a novel method to increase degree of constant volume was considered. Because the combustion speed is not infinity as assumed in Otto cycle but limited, it is necessary to decrease the piston-movement around TDC so as to increase degree of constant volume. At first, experimental study was made to confirm this. A test engine which has longer expansion stroke than compression stroke and enables a slow piston-movement during combustion period was built. The experimental data indicated an increase in degree of constant volume, but did not show an increase in thermal efficiency. In order to clarify this reason, numerical simulations are conducted in this paper. As a result, the gain due to the increase in degree of constant volume caused by piston-motion during combustion was found not exceeding the loss by increased heat loss.

In reciprocating internal combustion engines, the piston stops in a moment at top dead center (TDC), so there exists a necessary time to proceed combustion. However more slowing piston motion around TDC, does it have a possibility to produce the following effects? The slowed piston motion may expedite combustion proceed and increase cylinder pressure. This may lead to an increase of degree of constant volume. As a result, thermal efficiency may be improved. In order to verify this idea, two types of engines were tested. The first engine attained high cylinder pressure as expected. The P-V diagram formed an almost ideal Otto cycle. However, this did not contribute to the improvement in the thermal efficiency. Then the second engine with further slower piston motion by active piston control was tested in order to examine the above reason.

Honda developed a 750cm3 V-4 engine adopting an elliptical piston, and began selling the “NR” motorcycle with the engine installed in 1992. The adoption of an elliptical piston and cylinder achieved a compact layout of eight valves, which consists of four intake valves and four exhaust valves per cylinder. This paper explains the features of an engine with such a layout, focusing on the following: 1) Multiple valves and short-stroke enable the 750cm3 engine to achieve 15,000rpm. 2) The engine is more compact and lightweight than an engine having the same displacement, and more powerful than one with twice as many cylinders (8 cylinders). Also, this paper describes the techniques giving improved blowby gas and oil consumption characteristics as related to the sealing property of the piston, cylinder and piston ring and achieving performance equivalent to a conventional motorcycle engine.

The lean combustion system, developed for fuel economy inprovement, uses a Lean Mixture Sensor for the feedback control of air-fuel ratio in the lean mixture range. The Lean Mixture Sensor, comprises a zirconia solid electrolyte cell which has an electrochemical pumping action and a ceramic coating layer as a diffusion layer; the measurable range is from the stoichiometric to 25 of air-fuel ratio.

In order to improve thermal efficiency of spark ignition engines, the authors have studied means to improve degree of constant volume. The ideal Otto cycle realizes the maximal degree of constant volume with an instantaneous combustion at TDC. However, it is actually impossible to achieve instantaneous combustion as the combustion speed is limited. Thereby, the authors thought of an idea to increase degree of constant volume. That is to make the piston speed slow during combustion period by active piston-movement control, allowing more time for combustion. As a result, degree of constant volume was improved, but indicated thermal efficiency, estimated by integrating P-V diagram, was deteriorated. A longer expansion stroke was found to keep a longer period of high temperature and then, heat loss increased, leading to a decrease in indicated work.