The difference between gas and diesel engines.

Summary

• Gasoline is more refined than diesel, and ignites more easily and quicker, resulting in more power at the cost of more fuel.
• Diesel engines have higher compression ratios, combust without spark plugs, and provide better torque than gas alternatives.
• Gas engines spin faster with higher RPM and provide a smoother, quieter driving experience than diesel.

A gas car owner might not think about diesel too much. But whether you pull into the gas station or are shopping for a new car, the question “What is the difference between gas and diesel engines?” might pop into your head.

Both of these engines are known as internal combustion engines (I.C.E), meaning that they can turn chemical energy potential into mechanical energy. This energy forces the pistons to move within the cylinders, which then is transmitted to the wheels via the transmission. In simpler words, gas and diesel engines produce their power through a series of quick and controlled explosions within the combustion chambers, also known as cylinders. That being said, there are notable differences between these engines. Read on to learn about the features unique to each engine type.

To give you the most up-to-date and accurate information possible, the data used to compile this article was sourced from various manufacturer websites and other authoritative sources, including Car and Driver and Motor Authority.

Technical Differences Between Gasoline And Diesel Engines: Spark Versus Compression

Both gasoline and diesel are extracted and refined from crude oils. The first difference between them is that gasoline has to be refined more than diesel, which makes it thinner and more vaporous. This allows gasoline to be ignited easily and quicker, making it produce less power for the same amount of fuel burnt than its diesel counterparts. On the other hand, diesel is thicker and evaporates slower. This allows diesel to have 20% more energy density than gasoline.

Diesel Can Only Be Ignited Through Extreme Heat And Pressure

The biggest difference between these engine types is what happens during the power stroke in the four-stroke cycle, particularly during ignition. Both fuel types have a self-igniting temperature (SIT), which means the temperature at which the air-to-fuel ratio ignites through just temperature alone. When a piston compresses, the air inside pressurizes very quickly, meaning that it also heats up at the same time.

Diesel engines have higher compression ratios, which heats the air inside the cylinder significantly. This means that when diesel is vaporized in a cylinder, the fuel and air mixture is above its SIT, thus combusting without the need for a spark plug. Diesel will not ignite in a gasoline car, as the spark plugs will not be able to ignite the thicker fuel.

Gasoline Combustion Is Controlled By Spark Plug Timing

Gas engines must keep the inside temperature of combustion chambers below gasoline’s SIT, as the spark plug dictates when ignition occurs, instead of compression. In diesel engines, this is dictated by the fuel injectors. This naturally implies that gasoline engines have lower compression ratios than diesel alternatives to ensure a lower cylinder temperature. For example, a gas Audi A4 has a compression ratio of around 9:6:1, whereas a diesel variant stands at 16:2:1.

Different Ignition Methods Mean Different Parts

This means gasoline engines need to be equipped with throttle bodies. As pressure is applied to the gas pedal, the throttle body opens up its valves, allowing an adequate amount of air into the combustion chamber. More air requires more fuel, and as a result, more power is created.

Diesel engines, on the other hand, have implemented throttle controls instead. This allows the engine to very accurately dictate the amount of pressure that is created on the intake manifold.

Choosing The Right Type Of Engine

Both diesel and gas have very distinctive characteristics that make them both good and bad. The truth is, the best engine choice comes down to the intent of the owner. If the vehicle is going to be used less than 20,000 miles with minimal haulage, then gasoline will suit it just fine. But when we chuck in towing capabilities and long-term reliability, diesel might just have the edge.

Diesel Is Capable Of Powering The Transport Industry

Diesel engines can be found in a variety of vehicles, anywhere from consumer cars to semi-trucks and construction equipment. This is mainly due to their increased fuel efficiency, meaning lower running costs. Not only are they more efficient, but also more reliable. A diesel engine benefits from more torque at a much lower RPM compared to its gas alternatives. This allows the engine to produce the same amount of power at lower speeds, meaning less wear and tear on the engine over time.

Gasoline Provides A Better Experience With More Performance

One crucial factor determines the performance capabilities of each engine type — engine speed, also known as RPM. Horsepower, a measurement of an engine’s power, can be calculated as torque x engine rotation (RPM). Because gasoline ignites easier and quicker, a gas engine can spin faster without any ignition problems. The fact that they have a shorter stroke also massively helps in this case. This allows gas engines to produce a lot more power higher up in the range, as more fuel is burnt. In diesel engines, however, there comes an engine speed (usually around 4,000 RPM) where spinning any faster means the diesel mixture does not properly combust. This is why the torque curve on a diesel engine decreases drastically as you speed it up, more so than gasoline powertrains.

Pros And Cons Of Gas And Diesel Engines

The Pros And Cons That Come With A Diesel Engine

Pros:

• They boast higher fuel efficiency, giving more miles to the gallon compared to gasoline engines.
• They generate more torque, making them well-suited for hauling and towing heavy loads.
• Diesel has a higher energy density, offering more power for the same amount of fuel.
• Sturdier construction and lower RPM operation mean longer lifespans.

Cons:

• More expensive to purchase initially. Diesel fuel is also more expensive than gasoline.
• More nitrogen oxide and particulate matter are emitted, contributing to environmental problems such as global warming.
• Higher maintenance costs with complicated requirements for components such as fuel filters and emissions control systems.
• They produce more vibration and noise compared to gasoline engines.

The Pros And Cons That Come With A Gas Engine

Pros:

• More affordable to purchase initially compared to diesel engines.
• They are smoother and quieter than their diesel variants.
• Gasoline often tends to be cheaper than diesel fuel.
• Less maintenance work is required for similar components like fuel filters and emissions control systems compared to diesel engines.
• Less nitrogen oxide and particulate matter emissions are released into the atmosphere.

Cons:

• Lower fuel efficiency compared to diesel engines, offering fewer miles per gallon.
• They produce less torque, which makes them less suitable for heavy towing or hauling.
• Shorter lifespans compared to diesel engines because of their higher RPM operation and lighter construction.

Honorable Applications For Both Engine Types

Both of these engine types have been around for a very long time. Gasoline was used as far back as the late 1800s, with diesel trailing only a few years behind. It only makes sense that, throughout the years, there has been some serious use of both of these technologies. From race cars to cruise ship monsters, and to motorcycles, even, here are two of the most honorable applications for these fuel types.

Gasoline — Bugatti W16 Lineup

Turning heads is not necessarily easy nowadays with all the technology and advancements that we have made. Bugatti does not blend in with the ordinary though, as they have been a luxury carmaker for more than 120 years. Their latest W16 lineup consists of two eight-cylinder blocks put together at a 90-degree angle, featuring four turbochargers and 8.0 liters of displacement. This revolutionary engine was first brought out in 2005, debuting at the same time as the Veyron. It has since been updated to have an output of nearly 1,500 horsepower, with the most potent version being the Bolide, providing an outstanding 1,825 horsepower. It is the only 16-cylinder engine available on the market.

Diesel — Scania V8 Semi-Truck Engine

The Scania V8, industrially known as the DC16 085A, takes the crown for the most powerful semi-truck engine on the market, churning out 770 horsepower. The main selling point of this 16-liter powerhouse is the 2,730 pound-feet of torque it offers from only 1,500 rpm. Most commonly used in the hilly regions of Europe and Asia, Scania deserves a pat on the back for creating the ultimate work machine. Being a V8, it does not disappoint when it comes to its sound signature either.