# Diesel Engine

Model diesel fuel engine with throttle control, speed governor, and driveline output

## Library

Vehicle Components

## Description

The Diesel Engine block models a diesel-fuel, compression-ignition engine with a speed governor. The engine runs at a variable speed that you can control with a Simulink® throttle signal. The throttle signal directly controls the output torque that the engine generates and indirectly controls the speed at which the engine runs. If the engine speed exceeds the maximum speed that you specify, the engine generates no torque. The model does not include the air-fuel dynamics of combustion.

The block accepts the throttle signal through a Simulink inport. This signal specifies the engine torque as a fraction of the maximum torque possible in a steady state at a fixed engine speed and should lie between 0 and 1. A throttle signal below zero is interpreted as zero; above one, as one.

To prevent engine power and torque from becoming negative, the block imposes an upper limit on the maximum engine speed itself. If the maximum speed you specify exceeds this limit, the block issues an error that indicates what the upper limit is.

### Using Vehicle Component Blocks

Use the blocks of the Vehicle Components library as a starting point for vehicle modeling. To see how a Vehicle Component block models a driveline component, look under the block mask. The blocks of this library serve as suggestions for developing variant or entirely new models to simulate the same components. Break the block's library link before modifying it and creating your own version.

## Dialog Box and Parameters

Maximum power

Maximum power that the engine can output, in watts (W). The default is `150000`.

Speed at maximum power

Engine speed, in revolutions per minute (rpm), when the engine is running at maximum power. The default is `3500`.

Maximum speed

Maximum speed, in revolutions per minute (rpm), at which the engine can generate torque. The default is `4500`.

During simulation, if the engine speed exceeds this maximum, the engine torque drops to zero.

 Caution   If the engine exceeds its maximum speed, the engine block issues a warning.

## Engine Model

The engine model uses a programmed relationship between torque and speed, modulated by the throttle signal. An actual diesel engine does not have a throttle.

### Engine Speed, Torque, and Throttle

The engine model is specified by an engine torque demand function g(Ω) built into the block. It provides the maximum torque available for a given engine speed Ω. The block dialog entries (maximum power, speed at maximum power, and maximum speed) normalize this function to physical maximum torque and speed values.

The throttle input signal T specifies the actual engine torque delivered as a fraction of the maximum torque possible in a steady state at a fixed engine speed. It modulates the actual torque delivered τ from the engine: τ = T·g(Ω). The actual engine drive shaft speed Ω is fed back to the engine input.

### Engine Power and Torque Demand

The demand function g(Ω) is specified in terms of the steady-state engine power P(Ω).

The engine speed is limited to a maximum: 0 ≤ Ω ≤ Ωmax. The absolute maximum engine power Pmax defines Ω0 such that Pmax = P0). Define w = Ω/Ω0 and P(Ω) = Pmax·p(w). Then p(1) = 1 and dp(1)/dw = 0. Power is the product of torque and angular velocity. The torque demand function is thus

`${\tau }_{\mathrm{max}}=g\left(w\right)=\left({P}_{\mathrm{max}}/{\Omega }_{0}\right)\cdot \left[p\left(w\right)/w\right]$`

You can derive forms for p(w) from engine data and models.

The block uses a polynomial form for P(Ω):

p(w) = p1·w + p2·w2p3·w3

satisfying

p1 + p2p3 = 1 and p1 + 2p2– 3p3 = 0

Typical Engine Power Demand Function