Intake Fuel-mixture Heating
The multipoint injection requires no intake mixture pre-heating because this is formed only at the end of the inlet manifold or in the combustion chamber. It is only meaningful, in engines whose mixture is formed at the beginning of the inlet manifold, as in the case of the central injection, the single carburetor and the register carburettor. Here the fuel can condense on the cold walls of the inlet manifold thus, causing a certain amount of the ignitable mixture to be lost. This means that, during, and after cold starting, the mixture has to be made richer, which is reflected particularly, in a higher hydrocarbon content in the exhaust gas, and of course, in higher engine wear-and-tear and fuel consumption.
Mostly, directly below the throttle-valve(s), before the inlet manifold fans out to the individual cylinders, a "hedgehog" type element is mounted below. It's "quills" reach deep into the inlet manifold cross section. It is, first of all, electrically heated with a high amont of current (approx. 30 A), thus quickly warming the fuel-air mixture. Thereby, the condensation on the cylinder-walls is reduced.
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