How do gas engines differ from diesel engines?

The most important difference between diesel and gas engines lies in the ignition system.

The diesel engine is a compression-ignition engine. The high compression heats the air to such an extent that the injected fuel ignites on its own.

The gas engine, on the other hand, is a spark-ignition engine. The gas-air mixture is ignited by a spark from the spark plug, similar to a gasoline engine.

In both engine types, modern control systems precisely regulate the combustion process. For example, they determine the injection or ignition timing, thereby ensuring efficient and safe operation.

At first glance, the turbochargers in diesel and gas engines appear very similar. Their function is to supply sufficient oxygen for combustion.

In a diesel engine, only air is compressed and fed into the combustion chamber. A stationary gas engine goes one step further: here, the entire gas-air mixture is supercharged. Since many stationary power generation plants are operated at high loads for long periods of time, their turbochargers are specifically designed for this operating condition.

A key difference lies in the method of mixture formation.

In a diesel engine, only air is initially drawn into the combustion chamber and heavily compressed. The temperature rises to as high as 700 degrees Celsius. Only then is diesel fuel injected, which self-ignites due to the high temperature.

In a stationary gas engine, the air and gas are mixed before entering the combustion chamber. The mixture is then compressed and cooled.

Mobile gas engines often use what is known as multi-point injection. Here, air flows toward the cylinder first, before gas is precisely injected just before the combustion chamber. This allows engine power to be flexibly adjusted to meet specific needs.

Compression causes the temperature of the mixture to rise significantly. Therefore, it must be cooled before combustion.

In a diesel engine, this task is performed by an intercooler. In a gas engine, a mixture cooler ensures that the gas-air mixture is cooled to approximately 50 to 60 degrees Celsius.

An additional advantage: The heat dissipated in this process is not lost. It can be used, for example, in heating systems or district heating networks, thereby increasing the overall efficiency of the plant.

Not all gases are the same. Unlike diesel fuel, the composition and quality of gaseous fuels can vary.

This affects combustion characteristics and can, under certain conditions, lead to so-called knocking events. These result in uncontrolled combustion in the combustion chamber, which can damage the engine.

To prevent this, gas engines are equipped with a knock control system. Sensors detect unusual pressure or vibration patterns in the combustion chamber. The engine management system responds automatically, for example by adjusting the ignition timing, reducing power, or, in extreme cases, shutting down the engine.

There are also differences in power control.

In a diesel engine, power is primarily controlled by the amount of fuel injected. Stationary gas engines, on the other hand, often operate with a pre-mixed gas-air mixture. To flexibly meet power demands nonetheless, throttle valves are used to regulate the flow of the mixture.

Mobile gas engines also use throttle valves to precisely adjust pressure and mixture volume to the respective operating conditions.

From a niche product to a sought-after power source: The unique characteristics of gas engines make them a key component of modern energy supply systems.