WHAT IS SULPHATED ASH? Sulphated Ash (Sulfated Ash) is the percentage of oil that remains after burning it, treating the initial residue with sulphuric acids,…
The “right amount” is dependent upon both oil composition and engine operation.Ash accumulation can be affected by engine load. At full load, the butterfly valve (throttle) is wide open and creates positive air pressure in the intake manifold. Conversely at lower loads the throttle may be closed, creating a vacuum which pulls oil past the valve guides and into the combustion chamber. Counterintuitively, low loads will therefore lead to more ash buildup around the valve seat and face. This can reduce the life expectancy of the cylinder heads; if there is a requirement to run at low loads for operational reasons, an ashless oil may be a more appropriate choice that extends the life of engine components. Excessive ash can cause damage to the exhaust and aftertreatment systems. High ash is usually indicative of high levels of additives containing sulphur and phosphorous which (as in automotive applications) poison catalysts. In the combustion chamber, hot ash deposits can also act as ignition sources that ignite the air/fuel mixture independently of the spark plug and cause detonation. As a special case - two-stroke engines usually require an ashless oil because even the smallest amount of ash can clog up the intake and exhaust ports.
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