What Is the Difference Between Diesel and Gas?

June 28th, 2020 by

gas vs diesel engine

When you’re picking out a new vehicle, you have several factors you need to consider. You have to decide whether you want a sedan, truck, or SUV. You then have to choose what type of available features you want. You also need to consider whether you want a gas or diesel engine. However, you might then be wondering about the actual difference between gas and diesel. This helpful guide will go over the major differences between these two engines so you can decide which one is right for you.

The Invention of the Gas and Diesel Engine

The difference between diesel and gas engines starts with their invention. In 1876, Nikolaus August Otto invented the gas engine. This four-stroke combustion engine wasn’t particularly efficient. Only around 10% of the fuel was actually used to power the vehicle. The rest of the fuel simply produced heat. However, this gas engine offered the basic blueprint for modern car engines.

In 1878, Rudolf Diesel was studying engineering at Polytechnic High School when he learned about the poor efficiency of gasoline engines. He believed there had to be a more efficient solution, and he set out to discover it. In 1892, he invented and patented what was at that point called the combustion power engine. Today, we know it as the diesel engine.

Engine Operation

In the basic sense, gas and diesel engines have similar operations. Both engines use internal combustion and a series of rapid explosions within the engine to turn fuel into mechanical energy and propel a vehicle forward. The difference is how these explosions occur.

In a gasoline engine, the fuel mixes with air compressed by pistons. The spark plugs ignite this mixture to move the vehicle. On the other hand, in a diesel engine, the air is first compressed. This makes the air hot. The fuel then ignites when it hits the hot air.

Fuel Injection

Gasoline and diesel engines inject fuel in different ways. In a gasoline engine, fuel injection can occur two ways: a port injection system or a carburetor. The port injection system injects air into the fuel right before the intake stroke. In contrast, a carburetor mixes the fuel and air together before sending it into the cylinder to compress.

In a diesel engine, the fuel is injected directly into the cylinder. Since this process is a crucial part of how diesel engines work, the diesel injectors can become a complicated part of the process. In order to deliver the fine mist of fuel necessary for the process to work, the injectors must be able to withstand high temperatures and a large amount of pressure. To this day, engineers are working to make this system more efficient.

Examples of engine advancements include engine control modules and glow plugs. Engine control modules use numerous sensors to correctly time the injection, and a glow plug is a hot wire that can quickly raise the air temperature in a cold engine to help it start more efficiently.

Power Output

When you’re researching your new vehicle options, you might see a lot of talk about horsepower and torque. Horsepower is a measurement of power, and torque is a measurement of the twisting force on the driveline in the engine.

If your vehicle has plenty of horsepower but little torque, it will be slow to get moving. Torque is what gets vehicles going. Diesel engines tend to have higher torque but less horsepower. This is why sports cars usually have gasoline engines and big trucks typically have diesel engines. Sports cars need the extra horsepower that gasoline offers, and big trucks need that extra torque from a diesel engine to move heavy loads.

Differences in Efficiency

In addition to differences in power, another difference between diesel and gasoline engines is efficiency. Diesel engines tend to have higher fuel economy numbers when compared to gasoline engines. These higher efficiency numbers are mainly due to how the engines operate. A gasoline engine has to make sure it never reaches the self-ignition temperature during the compression stroke since this could potentially ruin the engine. As a result, a gas engine has to keep a low compression ratio.

Since a diesel engine doesn’t have fuel in the mixture during the intake stroke, it can compress the air more and have a higher compression ratio. A higher compression ratio equals better fuel efficiency.

Gasoline Fuel and Diesel Fuel

Since gasoline and diesel engines operate differently, they require different types of fuel. While both gasoline and diesel start as crude oil mined from the earth, the refining process then separates them into various types of fuels. Diesel fuel is thicker than gasoline, which means it evaporates slower. Diesel fuel also has more energy density.

These features are another reason why diesel engines tend to have better fuel economy than gas engines. While diesel fuel typically costs more than gasoline, most diesel engines require less of it to accomplish the same amount of work as a gasoline engine.

Plus, diesel engine owners have a new fueling option that’s becoming available to them: biodiesel. Biodiesel fuel is made from non-petroleum sources, such as vegetable oil. Converting a diesel engine to run on biodiesel requires some modifications, especially if you have an older engine. However, since efficiency and sustainability are becoming more popular, biodiesel might become the next common alternative fuel.


Since diesel engines operate without spark plugs and the electrical system needed to work the spark plugs, they have fewer parts that can malfunction. For the most part, diesel engines can deliver more miles and operation hours before they need any type of major service. Diesel engines also tend to have smaller repair bills when something does go wrong.

Now that you know more about the difference between diesel and gasoline engines, you should have an easier time deciding which one will suit your needs. When you’re ready to pick out your next new vehicle, contact Sweeney Chevrolet to take a look at all of your gas and diesel options.

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