Mazda defined the ideal state of the internal combustion engine and drew up a development process by backcasting from the ideal state. Through the process, the first-generation SKYACTIV gasoline and diesel engines were developed with the world's highest and lowest compression ratios respectively, which enabled the engines to achieve 15 to 20% lower fuel consumption. The internal combustion engine still has room for improvement and is expected to have higher thermal efficiency if specific heat ratio is increased by making an air-fuel mixture leaner, combustion period is shortened, and adiabaticity is enhanced. Mazda will continue to improve the efficiency of the internal combustion engine as this is a right approach to improving the earth's environment also from the perspective of reducing Well-to-Wheel CO2 emissions.
In recent years, significant reduction in GHG is required for passenger cars. Regarding the exhaust gas emissions, the RDE regulation, which acquires a more stringent measurement condition, is started in Europe. It seems the internal combustion engine field to be narrowing year by year. Many scenarios are shown the replacing electrification, but it is obvious sequentially transitioning and evolving while combining the internal combustion engine with electric power train. During this period, still internal combustion engine is required for higher efficiency and lower emission. In this paper, we introduce the combustion technology of Honda's present and near future gasoline engine. In addition, introduce the “HINOCA” which is original CFD soft wear developing in SIP project.
Toyota has been developing high thermal efficiency gasoline engines for the past twenty years for energy security and preventing global warming. Various combustion technologies were adopted to increase thermal efficiency at every launch of hybrid vehicles. Then, Toyota has developed new engines with common architecture concept, which is called as Toyota New Global Architecture (TNGA), based on the philosophy of developing ever-better vehicles. The target of new TNGA gasoline naturally aspirated engines was to achieve over 40% thermal efficiency and a high engine specific power simultaneously. In order to reach these targets, increasing the combustion speed was required. To realize this, stroke-bore ratio, intake port, and piston cavity shape were optimized. Additionally, injection spray shape and combustion strategy for catalyst heating was modified to meet upcoming PN regulations. Applying the common stroke-bore ratio realized similar combustion quality in the series of TNGA engines. On the other hand, reduction of CO2 emission has to be achieved on a “Well to Wheel” basis, considering the electrification of powertrain and the variety of fuel in the near future. For that purpose, an extensive approach is required incorporating not only auto-mobile industries, but also oil companies, governments and academic societies.
Current internal combustion engine situation seems to be similar with the dinosaur situation in the end of the Cretaceous period. After a powerful prosperity due to diversification and enlargement, dinosaurs are said to be extinct without being able to endure large environmental changes. Mammals, which were predator biological in weakness in the age of dinosaur prosperity, flourish in later times. The presence of current battery EV is reminiscent of Cretaceous mammals. Because of the historical knowledge, it is imagined that internal combustion engines will be extinct like dinosaurs and that BEV will prosper. However, there is the theory that it is said that the dinosaurs are extinct but part of them have survived and evolved into birds. The point of their survival and evolution is considered the following three factors of “Small and light”, “Homeothermic” and “Wings”. Here, hints on the survival of internal combustion engine want to be obtained from the evolution of dinosaurs.
Combustion kinetic modeling has long been expected to be, and is now becoming, a powerful tool for combustion engineering. In this article, fundamental aspects of the kinetic modeling will be introduced with a special focus on the technological prospects for clean and efficient combustion. Firstly, essential issues of the gas-phase thermodynamics will be described as it plays central roles in temperature variation and chemical equilibrium as well as the close relation to the statistical theory of chemical reaction rates. Secondly, the overview of the chain reactions, especially the branched chain reactions, will be discussed as behaviors of a system of reactions and thus a system of ordinary differential equations. Lastly the characteristics of the hydrocarbon oxidation as it shows NTC (negative-temperature coefficient) region and cool flame will be investigated in terms of the LTO (low-temperature oxidation) mechanism with the discussion of the possibility of controlling the cool flames.
Combustion characteristics of methane/hydrogen mixture are evaluated focusing on the NOx production by using numerical analysis of counterflow flames with evaluation parameters: molar ratio of hydrogen to methane “a”, combustion air temperature “Tair”, equivalence ratio ”er” and velocity gradient of counterflow “k”. As the increase in “a”, flame temperature becomes high, heat release rate becomes large, and eventually EINOxQ becomes larger in counterflows with a diffusion flame, a double flame, a twin flame, and a triple flame. With a larger “k”, strong flame stretch effect is obtained offsetting the EINOxQ increase even if with a large “a”. The counterflow with a diffusion flame for a lower air temperature shows larger fuel consumption rate, higher heat release rate, and lower flame temperature, resulting in lower emission index EINOxQ. The EINOxQ of counterflow with a double flame and a triple flame show local maximum values between 1 and 2 of “a”, being dominated by a result of the balance of total heat release rate “Q”, total fuel consumption rate and total NOx production rate. Among all the configurations of counterflow flames including planer one dimensional premixed flame, planer one dimensional premixed flame without flame stretch effect (er=1) shows the largest EINOxQ. The counterflow with a triple flame (er=1.2/0.8, k=666.7 s-1) with small “a”, the counterflow with a double flame (er=1.5, Tair = 500 K, k=666.7 s-1) and planer one dimensional premixed flame (er=1.5) with large “a” show the smallest EINOxQ. The counterflow with a diffusion flame (Tair =300 K, 500 K, k=666.7 s-1) shows the smallest Q and second largest EINOxQ. The planer one dimensional premixed flame (er=1) and the counterflow with a triple flame (er=1.2/0.8, k=666.7 s-1) show large Q.