To compare the performance of diesel engines of different sizes, cylinder dimensions, and power ratings, the parameter that can be used is the Specific Brake Fuel Consumption (SBFC).

1. Specific Brake Fuel Consumption (SBFC):
- SBFC is a measure of how efficiently an engine converts fuel into useful work. It represents the amount of fuel consumed per unit of power produced by the engine.
- It is expressed in units of fuel consumption per unit of power, such as grams per kilowatt-hour (g/kWh) or pounds per horsepower-hour (lb/hp-hr).
- By comparing the SBFC values of different diesel engines, we can assess their fuel efficiency and determine which engine consumes less fuel for the same power output.
- Lower SBFC values indicate better fuel efficiency and performance.

Other parameters that are commonly used to evaluate diesel engine performance but are not suitable for comparing engines of different sizes, cylinder dimensions, and power ratings include:

2. Swept Volume:
- Swept volume refers to the volume displaced by all the pistons in the engine during a complete cycle.
- It is a measure of the engine's capacity and is directly related to its size.
- Comparing engines based on swept volume alone may not provide an accurate comparison of their performance, as larger engines will naturally have higher swept volumes and potentially higher power outputs.

3. Air-Fuel Ratio:
- The air-fuel ratio is the ratio of the mass of air to the mass of fuel in the combustion chamber.
- It affects the combustion process, emissions, and fuel efficiency of the engine.
- While the air-fuel ratio is an important parameter for optimizing engine performance, it may not be suitable for directly comparing engines of different sizes and power ratings, as different engines may have different requirements for the ideal air-fuel ratio.

4. Volumetric Efficiency:
- Volumetric efficiency is a measure of how well an engine can fill its combustion chamber with air during the intake stroke.
- It is affected by factors such as intake system design, valve timing, and engine speed.
- While volumetric efficiency is an important parameter for evaluating an engine's breathing capability, it may not be directly comparable between engines of different sizes and power ratings, as different engines may have different design considerations and limitations.

In conclusion, the Specific Brake Fuel Consumption (SBFC) is the most suitable parameter for comparing the performance of diesel engines of different sizes, cylinder dimensions, and power ratings. It provides a standardized measure of fuel efficiency and allows for a fair comparison between engines with varying power outputs.