Intake Air Temperature sensor (IAT / MAT)
The airdensity consists of 2 components.
- The air pressure (measured with the MAP sensor)
- The air temperature
To measure the air temperature, we place a sensor in the intake path. Preferably not in the manifold. There the sensor could make an incorrect measurement due to the motor heating up. Somewhere for the gas valve is ideal.
Bosch IAT sensor
The sensor used is a so-called NTC thermistor. This sensor gives an X resistance at a Y temperature. The curve is not linear. We can program the characteristic of the sensor in the EFIgnition.
De NTC curve van de Bosch IAT
The air temperature sensor has a number of names:
Air Intake Temperature sensor (IAT)
Manifold Air Temperature sensor (MAT)
Together with the MAP sensor, we can determine the air density and therefore the amount of air entering the engine. If we calculate the airdensity, we see that in addition to the pressure, the temperature can have a major impact. The airdensity changes around 8% if the temperature drops or rises 20 degrees.
We must of course compensate for this. Otherwise, the engine will run lean in very cold air and too fat in very hot air. The adjustment curve is already included as standard in the EFIgnition base folder, but it is possible to adjust it.
De MAT correctie curve
Adjustment of ignition time based on MAT (Manifold Air Temperature)
The speed of combustion is influenced by the final compression temperature. If the intake air temperature is high, the combustion will proceed faster and we must allow the ignition to take place later in order to have the peak pressure above the piston on the right moment.
We can adjust the ignition time based on the measured air temperature. In this way we prevent the engine from detonating when the turbo warms up and thereby gives higher intake air temperatures.
The MAT-Based-Timing-Retard Curve