Detergents in gasolines are a big part of gasoline. Epa requires that a min of detergents be used in all gasolines which is known as the Lowest Additive Concentration (LAC).
Gasolines contain unstable components that can lead to deposit formation in the high temperature areas of the induction system, as many of you have seen when looking in one. The detergent additives are used in gas to reduce or eliminate deposit formation in the critical fuel delivery system components.
By reducing or eliminating these deposits , this can lead to improved engine power, better driveablility, improved fuel economy and reduced emissions. In most cases , gas marketers use these additives to differentiate their gas from each other.
Deposits also form in the higher temp conditions of the combustion chamber as well. The formation of these deposits can be influenced by the composition of the gas and the type of detergent additives used. Combustion chamber deposits (CCD) can result in increased Octane number requirement and increased NOx emissions.
Ok, Octane is a measure of the ability of a gas to resist knock. The antiknock value or a gas can be measured in two standard lab engine tests. Both use the same single cyl variable compression ratio engine attached to dynamometer. Different operating conditions characterize each method.
The D2699 measure the research Octane Number(RON) of gas and the D2700 measures the motor octane number(MON). Both tests, the engine compression ratio is adjusted to produce a measured level of knock with the test fuel. This gas is compared with the primary reference fuels producing slightly higher and slightly lower levels of knock. The octane number of the test fuel is determined by interpolating between the two primary reference fuels that bracket the test sample.
Of the two procedures, the MON test is more sever, correlating with high speed, high temp, part throttle conditions in a vehicle. The MON for most gas is lower than the less severe Ron test, which primarily correlates to a gasolines ability to resist run on or dieseling. The difference between the two ratings, (RON-MON) is called the sensitivity for the gas.
Some markets rate gas by the antiknock index(AKI) which is the average of the RON and MON values. (R+M)/2.
In the U.S. gas octane values are posted as AKI values on gas pumps. Other markets choose to express oct value as RON or MON only.
A vehicles octane requirement does not remain constant over its life. As the vehicle ages, octane number requirement(ONR) can increase from 1-13 octane numbers due to deposit buildup on the intake valves and in the combustion chambers. This is where deteregents come into play, and if you are able to run an engine on the lower octane with minimal knocking, then you're engine isn't having the deposit buildup as bad.
So, those that are having to step up their octane, are having more build up. Which ultimatly carbon on the valves, will cause excessive valves stem/guide wear giving a premature failure on the engine.
So, is additives needed? You bet.