Eiichi Murase

Initiation of Combustion in Lean Mixtures by Flame Jets

Flame jets produced by Pulsed Combustion Jet (PCJ) systems are particularly suited for initiating combustion in lean fuel-air mixtures. Presented here is a detailed investigation of performance characteristics of a PCJ system. The progress of combustion in the cavity of a generator was observed by schlieren photography of the events occurring in the interior of a rectangular cavity simulator fitted with transparent windows. Electric properties of the jet plume were measured by an electrostatic probe. Schlieren photographs revealed that products of combustion are discharged through the orifice before the combustion process can spread throughout the volume of the cavity. Signals of the electrostatic probe showed that ejection of incomplete combustion products from the cavity is principally governed by the duration of spark discharge. In the jet, the exothermic process decays at first and then becomes reestablished inside large scale vortex structures in the jet plume.

Performance of pulsed combustion jet at high pressures and temperatures

Abstract Ignition and combustion by Pulsed Combustion Jet (PCJ) at high pressures and temperatures were investigated using a compact rapid compression machine. The compression and stop motion of a compression piston in the rapid compression machine is controlled by the cam shape, and the cam is operated by a driving piston and compressed air. The combustion process was monitored by pressure measurements and high-speed schlieren photography. Lean limit of methane-air mixture was extended by PCJ, and the superiority of PCJ over standard spark ignition was demonstrated in enhancing the process of combustion in turbulent lean mixtures.

Ignition timing control of homogeneous charge compression ignition engines by pulsed flame jets

In diesel engines, most of the fuel is burned in a diffusion combustion phase, which inherently leads to the formation of excessive amounts of soot and NOx emissions. In order to decrease soot and NOx emissions simultaneously, the concept of a lean homogeneous charge compression ignition engine has been proposed. The onset of the combustion of the engine depends on the autoignition of the fuel, so it is quite difficult to control the ignition timing. On the other hand, it has been revealed that Pulsed Flame Jet (PFJ) has a great potential to enhance ignition reliability and burning rate in lean mixtures. In this article, autoignition characteristics of n -butane/air mixtures in a rapid compression machine (RCM) were shown first. The appearance of low temperature flames was observed in autoignition of n -butane in the RCM used here, and it was realized that the final compression conditions in the RCM correspond to the upper end of the low-temperature range of the positive temperature dependence region of ignition delay. Then the combustion tests with PFJ were carried out and it was demonstrated that the onset of combustion can be controlled by PFJ, and it was revealed that PFJ has a potential for the ignition timing control of the homogeneous charge compression ignition engine.

PHOTOGRAPHIC OBSERVATION AND EMISSION SPECTRAL ANALYSIS OF HOMOGENEOUS CHARGE COMPRESSION IGNITION COMBUSTION

ABSTRACT Experimental studies of homogeneous charge compression ignition (HCCI) combustion have been conducted by using a compact rapid compression machine. The image of the cool flame was captured by a high-speed camera with image intensifier, and during the cool flame appearance the Emeleus cool flame band was observed. Then blue flame became evident, its emission spectrum being similar to that of the cool flame with overlapping by HCO bands. During the main heat release duration, the hot flame emission spectrum was observed, where the distinct OH emission appeared, and it was superimposed on the carbon monoxide oxidation continuum. After the main heat release, the broad peak of the spectrum was shifted to the longer-wavelength side, and the images of the flames changed to red, especially at higher equivalence ratios. This red coloration must originate from the H2O vibration–rotation bands (580.7–966.9 nm). On the other hand, it has been revealed that a pulsed flame jet (PFJ) has the potential for directly controlling the start of HCCI combustion. In the jet of PFJ, the emission spectrum obtained was composed of distinct OH and CH emissions superimposed on the carbon monoxide oxidation continuum.

Plasma jet ignition in turbulent lean mixtures

In order to confirm quantitatively the performance and characteristics of the plasma jet ignition in turbulent lean mixtures, combustion tests were carried out in a disk-shaped combustion chamber with lean turbulent methane-air mixtures. In the tests, the governing parameters of the plasma jet ignition such as the plasma cavity size, the orifice diameter, and the discharge energy were varied. In this paper characteristic lifetime and a characteristic length of the plasma jet and an entrainment volume of the mixture into the plasma jet is defined theoretically and expressed by the parameters of the plasma jet ignition.

EFFECTS OF SPARK DISCHARGE MODE IN PULSED FLAME JET IGNITER ON OH FLUORESCENCE IMAGES IN A SWIRL FLOW

In internal combustion engines, lean burn is particularly attractive for minimizing pollutant emissions, in particular NOx, with a concomitant improvement in fuel economy. For combustion in lean fuel–air mixtures, achievement of adequate reliability of ignition and sufficiently high burning rate requires special methods. An effective technique is the injection of active radicals by means of the pulsed flame jet (PFJ) ignition system. Presented here is an experimental proof of the action of OH radicals produced by such an ignition system in a swirl flow with varying the spark discharge mode in the cavity of the PFJ igniter. The measuring apparatus used for this purpose was based on the planar laser-induced fluorescence method, and the effects of the spark discharge mode in the cavity of the PFJ igniter on the variation of OH fluorescence area in the jet and its intensity were revealed quantitatively.

PREDICTION OF IN-CYLINDER GAS MOTION IN ENGINES BY AN ENERGY METHOD.

A simple new method to predict in-cylinder gas motion during the compression stroke is presented for both flat piston and bowl-in-piston type combustion chambers. The method is principally based on the decay law of kinetic energy of the gas flow in an engine cylinder. Comparison of predicted and measured values shows fairly good agreement for different engine variables. Calculations for a flat piston type combustion chamber show that the velocity at TDC (top dead center) varies proportionally to the 1.15th power of the engine speed and to the -0.50th power of the compression ratio (CR). For the bowl-in-piston type combustion chamber, the ratio of the velocity in the bowl at TDC to that at the intake valve closure increases with a decrease in the CR, initial velocity, height of the bump clearance, and combustion bowl diameter, and with an increase in the engine speed.

A study on the direct control of the start of homogeneous charge compression ignition combustion by pulsed flame jet with rapid compression expansion machine

Aiming at direct ignition-timing control of homogeneous charge compression ignition in low-load conditions, pulsed flame jet, which is the jet of burning gas issuing from a small cavity facing a combustion chamber, was utilized. The characteristics of homogeneous charge compression ignition combustion initiated by pulsed flame jet were investigated using rapid compression expansion machine, which realizes single compression and expansion strokes and thus the measurement of indicated work. Higher indicated mean effective pressure was obtained using pulsed flame jet without increasing NOx emission drastically, and it was shown that pulsed flame jet has potential to control the onset of homogeneous charge compression ignition combustion appropriately. The validity of pulsed flame jet utilization was shown through pressure and NOx measurements.

OH fluorescence images of Pulsed Flame Jet in a swirl flow

Lean-burn spark ignition engines have the attribute of minimizing the emission of NOx and, concomitantly, maximizing fuel economy. For combustion in lean fuel-air mixtures, achievement of adequate reliability of ignition and sufficiently high burning rate requires special devices. The most effective among them is the injection of active radicals by means of the Pulsed Flame Jet (PFJ) ignition system. Presented here is an experimental proof of the action of OH radical produced by such an ignition system in a swirl flow with varying the spark discharge mode in the cavity of the PFJ igniter. The measuring apparatus used for this purpose was based on the Planar Laser-Induced Fluorescence (PLIF) method, and the effects of the spark discharge mode in the cavity of the PFJ igniter on the variation of OH fluerencence area in the jet and its intensity were revealed quantitatively.

Flame Extinction Behaviors in the Centrifugal Force Environment

By making use of the rotary cylinder combustion device which rotates with the combustible mixture in it, the real effects of the centrifugal force environment in the solid vortex on the flame behaviors are examined. The observed results show the enhanc-ed combustion by the swirl is not always expected, because of the rapid motion of a flame kernel to the swirl center, and the laminarization of turbulent flame. The propaga-tion speed of the flame initiated near the swirl center is considerably reduced, and in some cases, depending on the flame structure, vanishes to extinguish the flame.