Additional fuel injection (Hyundai Elantra XD)

On some versions of NOx catalytic converters, the additional fuel injection can lead to NOx afterburning. This results in the main fuel injection continuing for 200° after TDC during the power and exhaust strokes. Additional fuel injection ensures that a certain amount of fuel is supplied to the exhaust gases.

Unlike the pilot and main injections, the injected fuel does not ignite, but in the form of steam it takes the residual heat from the exhaust gases. During the exhaust stroke, the mixture of exhaust gases and fuel enters the exhaust system through the exhaust valves. Some of the fuel is returned to the cylinders via the EGR exhaust gas recirculation system for combustion, resulting in the same effect as pilot fuel injection. NOx catalytic converters use the fuel in the exhaust gas as an actuator to reduce the NOx content in the exhaust gas.

Since additional fuel injection results in dilution of engine oil, such injection must be approved by the engine manufacturer.

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