The initial specification to consider is the compression ratio of an engine.

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In a 4-stroke engine, there are four distinct phases:

1. Intake

2. Compression

3. Power

4. Exhaust

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Following the intake phase, where the fuel and air mixture enters the cylinder, compression precedes ignition by the spark. Compression brings the air and fuel molecules closer together, increasing their temperature for a more effective combustion process.

The compression ratio is expressed as a ratio such as 10:1 or 9.5:1, signifying the relationship between the volume of the cylinder when the piston is at the bottom of its stroke (maximum volume) and when it's at the top (minimum volume).

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Fuels are rated in octane and RON (Research Octane Number), with higher octane ratings indicating better resistance to premature combustion or knocking. However, why is there a need to resist combustion when the objective is to combust the fuel mixture? The reason lies in preventing knock, a condition where the fuel ignites prematurely due to compression alone, resulting in potential engine damage.

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Using high-octane fuel in a low-compression engine may result in unburnt fuel and exhaust gases that can obstruct the catalytic converter, foul spark plugs, and diminish power output. Conversely, utilizing low-octane fuel in a high-compression engine can induce knocking. Therefore, selecting the appropriate fuel type is crucial for achieving proper combustion timing.

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Here's a guideline for recommended octane ratings corresponding to engine compression ratios:

• Low compression (e.g., < 9:1): Regular octane (typically 87 RON)

• Medium compression (e.g., 9:1 to 10:1): Mid-grade octane (e.g., 89-91 RON)

• High compression (e.g., > 10:1): Premium octane (typically 91+ RON)

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It's important to recognize that the octane rating doesn't signify the fuel's power potential; rather, it denotes its resistance to knocking.