### The aim is 95% accuracy with 5% of the effort.

In 2006 we started the development of the engine simulation out of a personal interest as well as the than status quo in racing where much was regulated by air restrictors.

The goal of the Engine package in LapSim is the same as with the chassis simulation: easy to use, accurate and fast, supplying answers instead of raising more questions. It does not aim at analysing small details in the engine design. Its main purpose is concept analysis.

### Resistance model of poppet valves instead of flow figures

In order to keep the model practical for concept purposes, it was decided to develop a resistance calculation for the poppet valves, so one is not dependent on flow data.

The resistance calculation is mainly based on the area the poppet valve opens. Additional we added small correction factors dependent on lift.

### Camshaft model instead of measured camshaft data

In the camshaft menu you can describe the camshaft characteristics. Again we did not want to be dependent on camshaft data and decided to develop our own “optimal” camshaft profile generator, based on a couple parameters.

It is defined by 9 parameters per camshaft. In our view this should enable you program any 'logical' camshaft you might want to use. Again we decided to simplify for userfriendliness without sacrificing the accuracy.

### Spring-mass model to simulate gas dynamics

The model is a dynamic model, taking the inertia of intake and exhaust into account, dependent on their length and width. They are modelled like spring / mass system.

The intake dynamics can be seen in the figure. Grey area is piston travel. White line is the amount of air passing the intake valve. The orange line represents the cylinder pressure.

### Behaviour dependent on ignition, compression and fuel

The calculated amount of air/mixture captured by the cylinder is compressed, subsequently ignited and burned by a two zone burn model.

The speed at which the burning continues, is a variable and dependent on the momentary temperature of the air/fuel mixture.

Due to this, the model is capable of calculating the influence of advancing or retarding ignition, compression ratio and burn chamber geometry.

### combining the 4 fases, give 720 degrees pressure

With the two zone burn sequence simulated, a pressure diagram over the 720 degrees camshaft is available.

In these 720 not only the compression and the power stroke are calculated, but also the pumping losses of the exhaust and intake stroke.

### Engine torque calculated out integrated pressure diagram

The pressure diagram is subsequently integrated over the 720 degrees, giving in a generated torque of the model. The specified mechanical losses are subtracted from this value, resulting in a torque output.

Additionally the simulation model divides the amount of fuel by the power output, supplying an efficiency curve.