Question

Incomplete combustion of petrol or diesel in automobile engine produces (a) \(\mathrm{CO}\) and \(\mathrm{H}_{2} \mathrm{O}\) vapours (b) \(\mathrm{CO}\) and \(\mathrm{NO}_{2}\) (c) \(\mathrm{CO}\) (d) \(\mathrm{SO}_{2}\)

Short answer

The incomplete combustion of petrol or diesel in automobile engines produces (a) \text{CO} and \text{H}_{2}\text{O} vapours and can also produce (b) \text{CO} and \text{NO}_{2}.

Step-by-step solution

Understanding Incomplete Combustion

Incomplete combustion occurs when there is not enough oxygen to allow the fuel (hydrocarbons) to react completely to produce carbon dioxide and water. Instead, it produces carbon monoxide (CO) and sometimes soot (carbon particles).

Identify Products of Incomplete Combustion in Automobile Engines

In an automobile engine running on petrol or diesel, which are hydrocarbons, incomplete combustion typically produces carbon monoxide (CO) and water vapour (H2O). Additionally, nitric oxide (NO) can also be formed which can get further oxidized to nitrogen dioxide (NO2) in the atmosphere. Sulfur dioxide (SO2), while a common pollutant, is not a direct product of the combustion of pure hydrocarbons, it comes from impurities containing sulfur in the fuel.

Conclusion

With the provided options and understanding incomplete combustion in engines, the correct answer includes carbon monoxide (CO). The presence of water vapor is dependent on the hydrogen in the fuel, and nitrogen dioxide (NO2) can also be formed due to the nitrogen in the air and the high temperatures in engines.

Key concepts

Carbon Monoxide Production

Carbon monoxide (CO) production in automobile engines is a critical concern due to its toxic and potentially lethal effects. CO is a colorless, odorless gas produced by the incomplete combustion of fuel. Incomplete combustion occurs when the fuel, typically hydrocarbons from petrol or diesel, doesn't receive enough oxygen to fully convert to carbon dioxide (CO2) and water (H2O). Instead, it partially oxidizes and creates CO.

Factors contributing to incomplete combustion can include engine malfunctions, incorrect fuel-to-air ratios, and cold engine starts. When complete combustion is not achieved, not only is energy wasted but it also results in the production of unwanted CO, which can accumulate in the atmosphere and has severe implications for air quality and public health.

It's essential to control CO emissions through regular vehicle maintenance, ensuring optimal engine performance and thus, complete combustion. Technologies like catalytic converters help transform CO into less harmful CO2 before it exits the tailpipe.

Combustion Chemistry

Combustion chemistry involves the chemical reactions that take place when fuel is burned in an engine. The ideal reaction for hydrocarbon fuels, like petrol or diesel, requires a stoichiometric mixture - a specific ratio of fuel to oxygen that leads to the complete combustion of fuel.

The complete combustion chemical equation typically looks like this: \[ C_xH_y + zO_2 \rightarrow xCO_2 + \frac{y}{2}H_2O \] However, when there is insufficient oxygen or suboptimal combustion conditions, the chemistry is altered resulting in incomplete combustion, where the products can include: \[ C_xH_y + less\,oxygen \rightarrow CO + C (soot) + H_2O \] Automotive engines are designed to target complete combustion as much as possible, but inefficiencies and variable operating conditions can lead to incomplete combustion. Through the precise control of the air-fuel mixture and the use of various engine management systems, modern vehicles can optimize combustion chemistry to reduce the production of harmful byproducts.

Automobile Engine Pollutants

Automobile engines are a significant source of air pollutants, including a variety of harmful compounds besides those produced by incomplete combustion, such as nitrogen oxides (NOx), volatile organic compounds (VOCs), and particulate matter.

Nitrogen oxides are produced when combustion temperatures are high enough to cause a reaction between nitrogen and oxygen. NOx is a major contributor to smog and acid rain and can irritate the respiratory system. VOCs, on the other hand, are a range of chemicals that vaporize easily and can contribute to the formation of ground-level ozone, a harmful air pollutant.

Particulate matter, such as soot or ash, is made up of tiny particles that can penetrate the lungs and cause health issues. Efforts to reduce engine pollutants include technological advancements like exhaust after-treatment systems (such as particulate filters), improved fuel quality, and stricter emissions regulations. These measures are crucial for mitigating the impact of vehicle emissions on the environment and on human health.