الفهرس 
LITERATURE REVIEW
DISCUSSION OF THE RESULTSOnly 14 pages are availabe for public view
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Abstract
ventilation system is considered to be the major contributors to total engine oil consumption in internal combustion engine.
Piston rings play an important role in the performance and endurance of the engine. Piston rings have to provide optimum sealing function, low wear and friction all at the same time. The lube oil consumption and blow-by in an engine is directly related to the sealing function of the piston rings. Therefore, it is necessary to better understand the effects of clearance between piston and liner on engine lube oil consumption.
The literature can be divided into six categories; oil Consumption mechanisms, The Puddle Theory of oil consumption, oil consumption prediction, blow-by gases prevention, oil film thickness calculations and measurements and emission suppression.
The understanding of the oil consumption mechanisms in spark ignition engine will certainly help in explaining the effect of the different parameters on the rate of oil consumption and blow-by gases, yet theoretical modeling of the oil consumption is very difficult and research is predominantly experimental. Since experimentation is expensive, few published studies are available.
1.2- Oil consumption mechanisms
The oil consumption in the piston region has been investigated by means of both computer models and experimental measurements.
Gulwadi [1] noted that three different mechanisms of oil consumption occur in the ring pack system. Oil evaporates through the rings and the cylinder liner into the combustion chamber, oil is thrown off from the ring due to inertia, and gas blowing back towards the combustion chamber entrains oil from the ring pack. In all cases, the oil escapes from the cylinder with the exhaust gases. The evaporated oil trails behind or passes between the top ring and the liner during the down stroke. The amount of oil left behind on the liner is dependent on the scraping effect of the rings.
During the upstroke, the ring – pack lubrication is dependent on the oil film left on the cylinder liner during the down stroke. The top ring scrapes oil off the liner, and the oil is accumulated in front of the top ring. This accumulated amount of oil is thrown off the ring at TDC due to inertia. Throughout the engine cycle, oil is present in the ring pack area. This oil becomes entrained in the gases flowing to and from the combustion chamber. This entrained oil comes from accumulated oil at the ring-end gaps and the leading and trailing edges of the rings, from oil on the liner surface, and from oil on the groove surfaces.
Grzegorz [2] studied the influence of the axial clearance assembly of the top ring in its piston groove on blow-by and oil consumption in the diesel engine. He conducted these tests on four cylinders naturally aspirated - diesel engine.
Results of the experiments show that axial clearance of the top ring in its piston groove has a higher influence on the oil consumption than on the blow-by as shown in figure (1.1).
Even very large increase of axial clearance of the top ring, not occurring during normal operation, does not influence the blow-by at high rotational speeds and full load of the engine. This influence becomes more visible at lower speeds and is most significant at idling.
The increase of the axial clearance significantly influences oil consumption as shown in figure (1.1). The experiment does not allow direct explanation of the observed increase in oil consumption. This increase can be caused by more intense effect of oil pumping – it could indicate that first piston groove contains high amount of oil. But the most likely mechanism causing higher oil consumption seems to be oil transport in the gas stream blowing up to the combustion chamber. Higher reverse flow of gases for higher values of top ring axial clearance can be predicted taking into accounts that:
(a) Increase in axial clearance of top ring causes higher flow rate of gases around the top ring through the groove (calculations with the use of mathematical model of gas flow and ring dynamics).
(b) Top ring axial clearance, in described conditions of oil consumption measurements (full load at 3800 r.p.m), does not influence blow-by.
Since environmental demands are becoming even stricter regarding the exhaust emissions of internal combustion engines, the oil flow into the combustion chamber has to be reduced. As the oil control rings are one of the factors that control the oil flow through the ring pack, their optimization is important Tina et al. [3]. This optimization is made by computer modeling, as has been presented. The authors conclude, among other things, that the lubrication between the oil control ring rails and the liner is greatly affected by the twist of the ring.
Lacey and Stockwell [4] found that the oil consumption reduction actions are related to actions for emission suppression, as the consumed oil, or the oil trailed into the combustion chamber from the ring pack, directly affects the emissions of the engine.
Hydrocarbon emission are not only caused by lubrication oil that becomes entrained in the combustion gases flowing into and out of the ring-pack area, but also by the fuel-air mixture that flows into the crevices in the ring- pack region and remains there during combustion. During the exhaust phase, these gases flow out of the crevices and mix with the exhaust gas, thus adding to the amount of hydrocarbon in the exhaust gas, see Fig. (1.2).
During the blow-down process, unburned hydrocarbons from the ring crevice area move into the combustion chamber as the pressure falls, figure (1.2.a). At the beginning of the exhaust stroke, gases, including hydrocarbons, are wiped off from the liner wall and build up into a vortex, figure (1.2b). The vortex builds up even more at the end of the exhaust stroke, figure (1.2c), causing a significant amount of unburned hydrocarbons to leave the combustion chamber.