Kimitoshi Tanoue

Effect of autoignition characteristics of fuels on knocking properties

The correlation between the autoignition characteristics of n-butane/di-methyl ether/air mixtures and the knock intensity in a rapid compression and expansion machine was studied. The propagation velocity was obtained from the images of propagating flames at the moment of autoignition by a high-speed camera. The dimensionless parameters, ε and ξ, were used in the investigation, which are based on the theories of Zeldovich and Bradley. To obtain these dimensionless parameters, the numerical calculation using CHEMKIN-PRO with AramcoMech1.3 was carried out. The smaller gradient of autoignition delay time for n-butane with the higher amounts of di-methyl ether addition caused the higher flame propagation velocity and the resultant higher knock intensity, while significant differences of excitation times for autoignition heat release could not be seen. As a result, the gradient of autoignition delay time was concluded to have a strong influence on the knock intensities.

Enhancement of ignition characteristics of lean premixed hydrocarbon–air mixtures by repetitive pulse discharges

Abstract A newly developed small-sized inductive energy storage (IES) circuit that uses a semiconductor switch for the turn-off action is successfully applied to an ignition system in spark ignition engines operating under lean fuel–air ratios. This IES circuit can generate repetitive nanosecond pulse discharges. Experiments are conducted by means of a spherically expanding flame configuration for C3H8–air mixtures under various conditions. Findings show the investigated ignition system improves the inflammability of lean combustible mixtures in terms of extended flammability limits, shorted ignition delay time, and extended dilution limits, compared with conventional spark ignition systems.

Study of Extinction Properties in Dimethyl Ether Diffusion Flames (2nd Report, Effects of Kind of Inert Gases on Extinction Properties)

Experimental studies are conducted on extinction of non-premixed dimethyl ether (DME) flames stabilized in the counterflow configuration. Studies are carried out by injecting a fuel stream made up of fuel and inert gas (N2 or CO2 or Ar or He) from one duct an oxidizer stream made up of O2 and inert gas (N2 or CO2 or Ar or He) from the other duct. Critical conditions of extinction are measured by increasing the flow rate of the counterflowing streams until the flame extinguishes. Numerical studies are also performed using detailed chemistry at conditions corresponding to those used in the experiments and compared with measurements. The present study highlights the examination of the influence of equilibrium flame temperature, flame structure and kind of inert gas on extinction properties of DME. Results are compared and discussed in terms of Lewis number effect.

Studies of Fundamental Combustion Properties of Dimethyl Ether Flames(Thermal Engineering)

Recently there have been many problems related with automotive engineering, such as environmental issues and energy problems. These social circumstances motivate the adoption of urgent measures such as alternative fuel and new combustion techniques for the internal combustion engine. In this context, dimethyl ether (DME) is thought to be a potential alternative to diesel fuel due to lower overall pollutant emissions and more excellent fuel economy. DME has no carbon-carbon bonds and lowest possible carbon to hydrogen ratio after methane. The main features that make DME so attractive are : 1) the high oxygen content of 35% by weight, which provides smokeless combustion and high exhaust gas recycle tolerance ; and 2) the combination of a cetane number of 55 to 60 and a boiling point of-25°C, which provides fast mixture formation, reduced ignition delay, and excellent cold starting. Several recent publications have already presented results from diesel engines operated on pure DME. These experiments showed that DME is an excellent diesel fuel with a high cetane number. This fuel produces very low particulate emissions, while the NOx emissions are similar to those from current diesel fuel under the same engine operating conditions. This allows the engine operating conditions to be adjusted to reduce NOx without an accompanying increase in particular emissions. The purpose of this study is to clarify the combustion properties of DME/Air flames, which should be useful data for combustion modeling and simulation, using the spherical bomb that can embody the real engine conditions.

Effects of dilution with CO2 on Stretched Premixed Laminar Methane Flames

The purpose of this paper is to investigate the combustion properties of CH4/O2 mixtures diluted by CO2 compared to those of CH4/O2/N2 mixtures to study the feasibility of the new combustion method, which is expected to be effective in the NOx reduction and the improvement of combustion. Both experimental and numerical studies were conducted to scrutinize the effects of flame stretch on the burning velocity and the effects of flame instability which may play an important role in combustion performance not only for laminar flames but also for turbulent flames. In this study, experiments were conducted by using spherical combustion bomb for applications to internal combustion engines. First the effect of flame stretch was investigated experimentally and numerically and quantitative discussion was made in terms of Markstein number which means not-dimensional sensitivity of the burning velocity to flame stretch. As a result it has been found that Markstein numbers for both methane mixtures decrease with decreasing equivalence ratio. In addition CH4/O2/ CO2 mixtures have the low values of Markstein number compared with CH4/O2/N2 mixtures over the whole equivalence ratio.