Impact of Compression Ratio on Diesel Generator Engine Performance

The ratio of the maximum volume of the cylinder when the piston is at the bottom dead center to the minimum volume when the piston is at the top dead center is the compression ratio of the diesel generator. It indicates the degree to which the mixture is compressed. The compression ratio is a parameter that can basically reflect the working efficiency of the engine. For naturally aspirated engines, without considering other factors, an increase in the compression ratio means a corresponding improvement in engine performance and efficiency. However, the compression ratio cannot be too high, as this will cause knocking in the engine, which seriously affects the service life of the diesel engine. Therefore, it is often necessary to use high-grade fuel to reduce the possibility of knocking.

Engine with High Compression Ratio

If the engine has a higher compression ratio, it means that the mixture of oil and gas is compressed to a higher pressure and the temperature is relatively higher. The diesel in the mixture vaporizes more completely and is easier to burn. At the moment when the spark plug ignites after full compression, more energy can be released in a very short time. These combustion-generated energies are finally transmitted to the generator through mechanisms such as pistons and crankshafts, becoming the power for the generator to generate electricity.

Engine with Low Compression Ratio

In engines with a lower compression ratio, the fuel molecules do not vaporize as completely. Therefore, the combustion speed is relatively slow after the spark plug ignites. As a result, part of the energy is bound to be converted into heat energy, causing the engine temperature to rise instead of being completely converted into kinetic energy. So it can be said that with the same cylinder volume, a higher compression ratio means greater power output.

Overall, the higher the compression ratio of the engine, the higher the efficiency, better the performance, and better fuel economy. But the compression ratio of the engine is not as large as possible; it needs to be appropriate. An excessively high compression ratio will reduce stability and shorten the engine's service life. Designing an optimal compression ratio achieves a perfect balance among the engine's power, economy, and reliability.

Regarding the compression ratio issue of supercharged engines, many engines now adopt supercharging technology, which compresses air before sending it into the cylinder. In this way, the actual amount of air entering the cylinder is much more than that entering the cylinder in a natural state. Thus, the compression ratio of the engine is no longer the true one.

For supercharged engines, there are actually two compression ratios: one is the geometric compression ratio, calculated based on the geometric dimensions of the cylinder; the other is the actual compression ratio, which is the ratio of the actual amount of air entering the cylinder (converted to the natural state) to the combustion chamber volume. It can be seen that the actual compression ratio is greater than the geometric compression ratio.

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