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Diesel Performance 101

How Does a Diesel Engine Work?

Over the past ten to fifteen years, diesel engines and the vehicles they come in have exploded in popularity in the United States and throughout the world. Why is that? What makes the diesel engine such an economical, powerful and practical choice for so many drivers today? To understand the “why”, it’s important to understand how a diesel engine works. We’ll also look at three of the main differences between diesel engines and gasoline engines because a comparison will make it clear why diesel performance modifications are possible and ultimately so effective.

The first difference is the way in which gas and diesel engines use air. Gasoline engines take in a mixture of gasoline and air. Once taken in, that mixture is compressed and ignited with a spark from a spark plug. Diesel engines on the other hand take in only air. The air is compressed and then fuel is injected into the compressed air. When air is compressed its temperature increases, so the cause of combustion in a diesel engine is the heat of the compressed air. Once the injected fuel meets the heated compressed air it combusts spontaneously. This compressed air typically reaches temperatures of 700-900 °C or 1300-1650°F.

The second difference between gas and diesel engines is compression rate. Compression rate is a huge factor in both the efficiency of the diesel engine and the ability to get more horsepower out of it. Typical gasoline engines have a compression ratio of between 8:1 and 12:1; diesel engines, on the other hand, typically range anywhere from 14:1 and as high as 25:1. The higher compression ratio of a diesel engine allows it to perform much more efficiently. To further aid a diesel engine in the compression and cooling of intake air, turbochargers and intercoolers are added to most diesel engines.

Fuel injection is the third main point of difference between diesel and gasoline engines. Gasoline engines usually use one of two methods, either carburetion or port fuel injection. With carburetion the air and fuel is well mixed before it enters the cylinder. With port fuel injection the fuel is injected right before what is called the intake stroke, and occurs outside of the cylinder where the combustion will occur. Diesel engines use direct fuel injection. Diesel fuel is injected directly into the cylinder where the combustion is occurring. Of course, the injector itself must be able to withstand both the temperature and the pressure inside of the cylinder while still being able to deliver the diesel fuel in a mist that is fine enough to allow for combustion. Part of getting that mist to combust is proper mist circulation in the cylinder so that it is evenly distributed. To aid in fuel circulation diesel engines have special induction valves or pre-combustion chambers.

Perhaps the largest difference in the diesel engine vs. the gasoline engine is the injection process as a whole. Since gasoline engines mix air and fuel and ignite that combination with a spark plug, they are limited by low compression ratios. If the air and fuel mixture is too compressed, the mixture will spontaneously ignite, which will cause a knocking sound. Because diesel engines are compressing only air the compression ratio can be much higher and higher compression equals more power!

So now that you understand how a diesel engine works, it’s time to take a look at some diesel performance upgrades for your vehicle! Here’s a brief list of the most common. If you would like to learn more about these upgrades, check out our Frequently Asked Questions section.

A. Cold Air Intakes – Diesel engines are all about air — the more of it and the cooler it is, the better. With the addition of any diesel performance chip, performance module, or diesel programmer; increasing air-flow is critical to higher horsepower gains without losing fuel mileage as well as extending the life of your turbo diesel engine.

B. Tuners, Chips and Programmers – Gaining more horsepower has never been easier. Most of our performance chips are plug and play or can be installed in under an hour.

C. Diesel Exhaust Systems – Back Pressure and high exhaust temperatures are two of the easiest ways to hurt your engine’s life.

D. Diesel Gauges – Monitoring your engine’s performance is one of the most important things you can do. The most important diagnostic to pay attention to is your exhaust temperature gauge. If you are more interested in performance you will want to monitor your turbo boost with a boost gauge and your exhaust temperature with a pyrometer gauge.