Question

The air requirement of a petrol engine during starting compared to theoretical air required for complete combustion is
A) More
B) Less
C) Same
D) May be more or less depending on the engine capacity

Answer 1

We know that combustion is a chemical process in which a substance reacts rapidly with oxygen and gives off heat. The original substance is called the fuel, and the source of oxygen is called the oxidizer. The fuel can be a solid, liquid, or gas, although for airplane propulsion the fuel is usually a liquid. Spontaneous combustion can occur when a substance with a relatively low ignition temperature (hay, straw, peat, etc.) begins to release heat. Combustion begins if sufficient oxidizer, such as oxygen, and fuel are present to maintain the reaction into thermal runaway.

Step-by step answer:
We know that for proper burning or combustion of fuel (petrol) engines require oxygen, and this oxygen is supplied to the engine by atmospheric air. The ratio of mass of air sucked by engine to mass of fuel injected is air-fuel ratio. If exactly enough air is provided to completely burn all of the fuel, the ratio for fuel (SI engine) is 14.5:1.
It should be known to us that complete combustion happens when there is a good supply of air. Carbon and hydrogen atoms in the hydrocarbon fuel react with oxygen in an exothermic reaction: carbon dioxide and water are produced. energy is given out.
The air requirement of a petrol engine during starting compared to theoretical air required for complete combustion is less.

Hence, the correct answer is Option B.

Note: We should know that exothermic reactions are reactions or processes that release energy, usually in the form of heat or light. In an exothermic reaction, energy is released because the total energy of the products is less than the total energy of the reactants. An exothermic reaction occurs when the temperature of a system increases due to the evolution of heat. This heat is released into the surroundings, resulting in an overall negative quantity for the heat of reaction.
On the other hand, endothermic reactions are chemical reactions in which the reactants absorb heat energy from the surroundings to form products. These reactions lower the temperature of their surrounding area, thereby creating a cooling effect. An endothermic reaction occurs when the energy used to break the bonds in the reactants is greater than the energy given out when bonds are formed in the products. This means that overall, the reaction takes in energy, therefore there is a temperature decrease in the surroundings.