What Is Compression Ignition?

The Starting Power of Diesel Engines

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The concept behind compression ignition involves using the latent heat built up by highly compressing air inside a combustion chamber as the means for igniting the fuel. The process involves compressing a charge of air inside the combustion chamber to a ratio of approximately 21:1 (compared to about 9:1 for a spark ignition system).

This high level of compression builds tremendous heat and pressure inside the combustion chamber just as fuel is primed for delivery. An injection nozzle plumbed into the combustion chamber sprays a mist of precisely metered fuel into the hot compressed air whereupon it bursts into a controlled explosion that turns the rotating mass inside the engine. ​

Compression ignition is also commonly referred to as diesel engine, largely because it is a staple of a diesel ignition. Gasoline requires the spark ignition in order to start, but diesel can be started through this alternative means of ignition.


Along with the added start-up power of the much stronger compression ignition, the general wear-and-tear on an engine is significantly less than that of a gasoline engine, meaning less maintenance and upkeep on your diesel vehicle. Because there is no spark ignition, the absence of spark plugs or spark wires means less cost in that department as well. They're also more efficient than gas engines in converting fuel to power, resulting in better fuel economy.

Since diesel also burns cooler than gasoline, units running on compression ignition tend to have a longer lifespan than those running on spark ignition and gasoline. Overall, this makes the engine also more durable and reliable than gas models. If something goes wrong with a diesel engine, it's not going to be the compression ignition — at least not for a long time. That's not the case with spark plugs and wires which often need to be replaced in gasoline engines, rendering the vehicle unable to start.

Common Uses

Compression ignition is commonly used in power generators as well as mobile drives and mechanical engines. Most often seen in diesel trucks, trains, and construction equipment, this type of engine is found in almost every market industry. From hospitals to mines, the use of compression ignition acts as a backup and primary power source for much of the modern world. 

Chances are, if you've ever been in a snowstorm that knocked out the power and heat, you've probably used a compression ignition engine to start your backup generator. Even the food you eat is often brought here by compression ignition cargo or freight ships. The mail you get delivered by FedEx and UPS is also run on diesel engines! 

Public transit services like buses and some city trains use diesel to power their engines as well, resulting in long-term fuel economy and less waste. However, many cities and automobile manufacturers have begun switching to electric engines to further reduce energy waste and fuel consumption. Still, when the power's out, you can always rely on the efficiency of compression ignition to restart the generator back up and get the lights back on.