**2. Gasoline automotive engines**

The gasoline automotive engine works by injecting a mixture of gasoline and air in the combustion chamber and after compressing them the timing of the combustion is just as the piston arrives at the top dead centre (highest point in the combustion chamber). The combustion timing is induced by a spark which causes a rapid rise in temperature and pressure which in turn push the piston down again turning the camshaft which translates this rotational motion into linear motion used by the vehicle. Thus in an ideal engine the reactants would all ignite with the spark instantaneously and thus it is called the spark ignition engine.

This cycle is called the Otto-cycle which is shown as follows together with the relative P-V diagrams:

Intake stroke is performed by an isobaric (same pressure) expansion of fuel/air mixture represented by point 1 to point 2 (**Figure 1**).

Followed by an adiabatic (no heat exchange) compression stroke represented by point 2 to point 3 (**Figure 2**).

Ignition starts power stroke isochoric (same volume) process shown by point 3 to point 4 (**Figure 3**).

Adiabatic expansion process follows, characterizing the power stroke as per point 4 to point 5 (**Figure 4**).

The exhaust stroke is characterized by isochoric (constant volume) cooling compression processes as per point 5 to point 6 (**Figure 5**).

And the cycle is completed by an isobaric compression as represented from point 6 to point 1 (**Figure 6**).

**Figure 1.**

*Drop of piston pulls in gas mixture from carburettor.*

**Figure 2.** *Return of piston compresses fuel mixture adiabatically.*

*Quality and Trends of Automotive Fuels DOI: http://dx.doi.org/10.5772/intechopen.94167*

#### **Figure 3.**

*Fuel ignition causes rapid rise in temperature and pressure.*

#### **Figure 4.**

*The power stroke: the adiabatically expanding gases do work on piston.*

#### **Figure 5.**

*The exhaust valve opens as the piston reaches the bottom of its travel dropping the pressure to atmospheric pressure.*

#### **Figure 6.**

*Rise of piston drives out burned gases. Exhaust valve closes at 1 and intake valve opens.*
