please explain the chart below what is the dot represent an

please explain the chart below ? what is the dot represent and why is it going down ?

Solution

In the case of an IC engine throttle represents the opening of inlet manifold. As you apply accelerator in an automobile what actually happens is that you are opening the inlet manifold. i.e. applying accelerator is opening of throttle.

Here the graph represents the variation in fuel consumption with the throttle position ( Probably this must be for a constant load)

Initially when the engine is just started and the engine is idling ( i.e. when you havent applied the accelerator yet ) the engine consumes more fuel. Because during the start the engine could be in cold condition, fuel wont vapourise easily so the more fuel is required for proper mixing of fuel and air. And also initially the friction will be higher compared to a running condition. So to get a specific speed more energy has to be given to engine to counter this frictional losses and also to overcome the improper mixing behaviour

But as the vehicle/ engine starts working gradually the temperature of the manifolds will increase and the fuel will vapourise easily and form the required air-fuel mixture easily without much loss of fuel. So the fuel consumpiton will get reduced . And compared to the idling case, the percentage of frictional loss will be lesser during running condition. So for a given load the fuel consumption will get reduced as you give more throttle.

[ NOTE : But if the load on the engine increases, fuel consumption will increase ]