Effect of Lubricant Composition on Combustion-Chamber Deposits 540237
MOLECULAR weight or volatility has been found to be the most important factor in determining the extent to which a lubricant contributes to combustion-chamber deposits and octane requirement. Bright stock appears to be particularly harmful. Crude source (or variation in predominating hydrocarbon type) seems to have little effect.
These authors report further that commercially practical mineral-base oils have been developed that show a significant advantage over previously known conventional lubricants in their ability to prevent these deposits and octane requirement increase when used with a conventional leaded fuel. Moreover, they say that SAE 5W-20 motor oils can be made that give a 4-5-octane advantage over conventional motor oils in preventing detonation.
They point out, further, that, although progress has been made, even better lubricants and fuels are needed, in this respect.