Exhaust constituents of a petrol (gasoline) engine Under normal operation, which set correctly represents key constituents present in the exhaust gas of a spark-ignition petrol engine?

Introduction / Context:
Petrol engines combust hydrocarbon fuel with air. Real-world combustion is never perfectly complete, so the exhaust contains a mixture of desired and undesired species. Recognizing major components is fundamental to emissions control and after-treatment design.

Given Data / Assumptions:

• Conventional petrol engine with three-way catalyst (may be warming up or at stoichiometric).
• Typical pump gasoline without high ethanol fraction.
• Normal load and temperature conditions.

Concept / Approach:
Combustion of hydrocarbons produces carbon dioxide and water. Due to mixture variations, there will also be carbon monoxide (from incomplete oxidation), unburned hydrocarbons (fuel vapours), nitrogen oxides, residual oxygen, and nitrogen. Therefore, petrol vapours, water vapour, and carbon monoxide are all present to some extent.

Step-by-Step Solution:

Verification / Alternative check:
Gas analyzers routinely measure CO, HC, CO2, O2, and NOx in inspection and diagnostic procedures, confirming the mixture of species.

Why Other Options Are Wrong:

• Single-component answers are incomplete.
• Only nitrogen and oxygen: ignores products and intermediates of combustion.

Common Pitfalls:
Assuming a fully warmed catalyst eliminates all CO and HC; during warm-up and aggressive transients, these still appear.

Final Answer: