Michio Kitano

Examination of lubricant oil components affecting the formation of combustion chamber deposit in a two-stroke engine

Abstract In this study, influence of fuel and lubricant oil components on the combustion chamber deposit (CCD) formation was investigated using both a two-stroke engine and an autoclave. The results obtained show that the influence of lubricant oil on CCD formation was greater than that of the fuel and most CCD was formed from the detergent dispersant added to the lubricant oil. In particular the metallic detergent formed a larger amount of CCD than the ashless dispersant. The influence of deposit formation under the low-pressure condition on CCD accumulation at the engine appeared to be greater than that of deposit formation under the high-pressure condition.

A Study of Combustion Chamber Deposit Formation in Small Two-Stroke Cycle Engines

Using an autoclave and a small two-stroke cycle utility engine, we studied influences of fuel and lubricant oil on combustion chamber deposit (CCD) formation. The autoclave results showed that there was some specific temperature/pressure region that made the deposit maximum. On the other hand, the accumulated CCD weight on the piston crown surface of the engine was measured, and the relative contribution of the fuel, lubrication oils and oil additives to the CCD accumulation was discussed. In conclusion, most of the CCD was formed from the lubricant oil, especially the oil additives. Furthermore, we measured temperature profiles on a piston crown surface using fusible plugs that had specific different melting points and discussed some aspects of their relations to the autoclave results. We found that the surface temperature of the piston crown was roughly the same as the autoclave temperature region when the CCD was formed. Introduction It has been known that the combustion chamber deposit (CCD) on a spark ignition engine makes various problems such as an increase in the octane-number requirement [1], a NOx emission in the exhaust gas [2] and change in thermo-mechanical conditions of engine cylinders and pistons [3]. The CCD accumulation on the two-stroke cycle engine is greater than a four-stroke one, because the former has the unique mechanism that supplies fuel and lubricant oil together into the cylinder and burns them in it. The CCD accumulation spoils performance and reliability of the engine and is disadvantageous in the circumstances where severer emission regulations have been applied to mopeds and utility engines. Accordingly, reduction of the CCD accumulation is one of the most important problems to be solved, without negligence of various advantages of two-stroke engines. We investigated the relationship between operating conditions and the CCD accumulation in a two-stroke engine 4 . In contrast, most previous experiments on the CCD formation were conducted using only an autoclave that offers the circumstances of the high temperature and pressure without combustion 5,6 ; it simulates the quench area near the combustion chamber wall. Furthermore, most studies on the CCD formation dealt with a four-stroke engine, while only a few studies were made using a real two-stroke one. In this study, both an autoclave and a small two-stroke engine were made use of to conduct experiments for CCD formation. The influence of temperature and pressure in an autoclave on deposit formation from oils and additives were investigated. The CCD on the piston crown surface also was measured under the constant running conditions. The relative contribution of lubricant oils Key Engineering Materials Online: 2003-07-15 ISSN: 1662-9795, Vols. 243-244, pp 225-230 doi:10.4028/www.scientific.net/KEM.243-244.225

The Combustion Chamber Deposit Formation on a Piston Crown of a Small Two-Stroke Cycle Engine

We studied the influence of fuel and lubricant oil on the combustion chamber deposit (CCD) formation using an autoclave and a small two-stroke engine. The autoclave results showed that there were some temperature and pressure region that made a maximum deposit formation. On the other hand, the CCD weight on the piston crown surface of a utility two-stroke cycle spark ignition engine was measured, and the relative contribution of fuel and lubricant oil to the CCD formation was discussed. The engine was operated with gasoline as a fuel and with commercial oil for two-stroke and base oil without any additives as lubricant oil. As a result, most CCD was formed from lubricant oils, especially oil additives. Furthermore, we measured the temperature profiles on a piston crown surface using many fusible plugs that had specific melting points, for considering the relation between the engine CCD and the autoclave results.

Lewis Number Effects on Flame Temperature of Coaxial-Flow Diffusion Flames.

Lewis number and preferential diffusion effects on the flame temperature of coaxial-flow diffusion flames were examined. Flame analysis based on the flame sheet model shows that the flame is strengthened when Lef>1 or LeO 1, where Lef and LeO are the Lewis numbers of fuel and oxygen, respectively. This is caused by the increase or decrease in the total enthalpy in the flame due to the difference in diffusion rates between heat and reactants, and indicates that flame extinction at the flame tip (tip opening) might occur when the flame is weakened. It further shows that for a mixed fuel with two components having different Lewis numbers, Lef1 and Lef2, component stratification by preferential diffusion occurs and mixed Lewis number effects become increasingly separated in the downstream direction. Therefore, in the case where Lef1>1 and Lef2<1, preferential diffusion might bring about the minimum value in the flame temperature profile and lead to the local blow-off which was observed experimentally.

Soothing Limit of a Double Diffusion Flame

Inside a coaxial flow diffusion flame of the ordinary type (fuel ejection into an air atmosphere), another diffusion flame of the reverse type (air ejection into a fuel atmosphere) was formed. The sooting limits of this double diffusion flame were measured for propane with three different types of burners, and the effect of several factors, such as the amount of inner air, flame-to-flame distance, thermal condition between the two flames, and flow stretch, were investigated. On the basis of the results, the effectiveness of making use of the double flame in the suppression of soot emission from diffusion flames of the coaxial flow type was discussed. The main findings were : (1) The double flame condition suppressed soot emission more effectively. (2) The sooting limit was controlled by the outer flame temperature, and therefore, adjusting the factors so as to increase this temperature may lead to much stronger soot suppression.