Diesel or petrol: How do they differ, and which is better?
Diesel or petrol? This topic will never get old as long as these types of engines stay in cars. Every day when one opens a car forum, one encounters questions like - diesel or petrol, petrol vs. diesel, diesel vs. petrol, and our favorite one is: Is diesel or petrol better?
Of course, these topics are very popular, and many users decide to give advice or at least highlight the advantages of one and the other type of engine. However, a short discussion is always followed by an exchange of opinions and stormy communication with a lot of swearing and insults, which ends with sentences that diesel belongs to tractors and petrol to lawnmowers.
Table of Contents
- Diesel vs gasoline
- Diesel or gasoline?
- So is diesel or petrol better?
- Advantages and disadvantages of a diesel engine
- Advantages and disadvantages of a gasoline engine
Enough of unnecessary talk. Let's talk about these two engines, compare their advantages, disadvantages, maintenance costs, and everything else, and decide whether diesel or gasoline is better.
There are only two groups of people. One group cannot afford a diesel engine, and the other a petrol engine. Diesel is particularly praised for their low consumption and pull at low revs.
Petrol enthusiasts, conversely, get higher power distributed evenly across the whole range of revolutions and the possibility to turn the engine to high revolutions.
In the 90s, the choice was clear. Those who wanted to drive slowly and for consumption chose diesel, and those who demanded dynamics from the car without looking at consumption reached for a car with a gasoline engine.
Today, however, times are completely different, and determining whether diesel or gasoline is better is not easy but not impossible. But let's first look at the three basic differences between diesel and gasoline engines.
Diesel vs gasoline
Spark vs. compression:
The basic difference between these two engines is how the mixture is ignited. Of course, let's take it as if we are only talking about car engines, wherein in most cases, it is true that a spark-ignition engine equals a petrol engine and a compression-ignition engine equals a diesel engine.
Related article - Petrol Engine: How does it work, and what are its advantages?
A gasoline engine does not always have to be a gasoline engine. A good example is, for example, gasoline engines from Mazda called Skyactiv-X or other gasoline engines, denoted by the abbreviation HCCI (Homogenous Charge Compression Ignition), which means that the mixture in the combustion chamber is homogeneous. Its ignition occurs due to the high temperature formed during compression.
In most cases, however, the gasoline engine is a spark-ignition engine, which means that a spark from a spark plug ignites the mixture of fuel and air.
Related article - Diesel Engine: How does it work, and what are its advantages?
A compression-ignition engine doesn't always have to be just a diesel engine. For example, a Stirling engine or Hot-bulb engine, also called semi-diesel, can burn other fuel types. However, in the case of car engines, as I mentioned before, it is overwhelmingly true that a compression-ignition engine is also a diesel engine.
And as we all probably know, a diesel engine ignites a mixture of fuel and air due to the high compressed air temperature in the combustion chamber.
Another difference between the two engines is the way power is regulated. In the case of a gasoline engine, power regulation is most often carried out using the throttle valve.
The accelerator pedal is either electronically or using a cable connected to the engine's throttle valve. Pressing the accelerator pedal opens the valve, and more air flows into the engine.
Related article - Throttle valve: How it works and its possible malfunctions
In this way, the amount of air intake is regulated, according to which the engine control unit adjusts the fuel dose. Regulation of petrol engine performance does not have to occur only with the throttle body's help. Some gasoline engines have variable timing and valve lift technology that can replace the throttle function.
Diesel engines, in most cases, are not equipped with a throttle valve, so the amount of injected fuel influences the regulation of engine performance. By depressing the accelerator pedal, we control the amount of injected fuel and engine speed.
The throttle valve in diesel engines primarily serves for better regulation of vacuum in the intake, more efficient EGR valve function, and smoother engine shutdown.
Fuel vs. air:
You must have already read here or somewhere else that the ideal coefficient of excess air and fuel is 14.7 to 1, which is equal to a stoichiometric mixture. This means that 14.7 kilograms of air are needed to burn 1 kilogram of fuel perfectly.
In conventional naturally aspirated petrol engines, the control unit maintains the excess air ratio between approximately 12:1 and 17:1. However, turbo-petrol engines can also go for a lower ratio. This only applies to gasoline engines.
Related article - Air-fuel ratio: How does it affect engine performance?
Diesel engines can operate with a much wider ratio of excess air, which is precisely the reason why the performance of a diesel engine can be regulated by the amount of fuel injected for the same amount of air, as we mentioned in the previous point.
For diesel engines, this ratio can be between 16:1 and 70:1, which means that much less fuel can be injected for the same air volume than a gasoline engine. Thanks to this, diesel engines achieve their magical, low fuel consumption.
These are the three basic differences between petrol and diesel engines. But which one is better? Is diesel or gasoline better? Let's compare them and say something about their advantages and disadvantages.
Diesel or gasoline?
Dynamics and performance:
As mentioned, in the 90s, the choice was straightforward. Those who wanted dynamics had to reach for a car with a gasoline engine. In today's age of turbocharging and direct injection, the choice is more difficult. Diesel engines stand out with a strong pull even at very low revs thanks to their high torque, but at higher revs, they don't have as much power as their petrol cousins.
Related article - Engine Power And Torque: Which of these parameters is more important?
The development of gasoline engines does not stand still. Turbocharging and variable valve timing technologies are almost a matter of course. Petrol engines, however, can compete with diesel engines at low revs.
Related article - Horsepower: What is it, and why is it important?
In any case, it is clear that if we compare two engines of the same volume equipped with the same technology, the petrol engine will be the clear winner in terms of dynamics and performance.
Sound and running culture:
Although diesel engines' sound and operation constantly improve, there is still a significant difference compared to petrol engines. A diesel engine will never be as refined as a petrol engine and will never have the same sound. So, gasoline is the obvious choice if you cared above all about sound and refined running.
Gasoline for a sprint and diesel for a marathon:
Although this trite sentence hides a lot of true information, it tells about the situations in which a car with a diesel engine and a car with a gasoline engine are suitable. When deciding between a diesel and gasoline car, you should first consider where you drive, or how long your routes are. Why?
Related article - Cold Engine: What happens in the engine as it warms up?
A gasoline engine warms up much faster than a diesel engine, which is important in comfort and fuel consumption. At the same time, if the engine is cold or not warmed up to its operating temperature, the wear of the moving parts of the engine increases. Short drives during which the engine does not have time to warm up are therefore not very beneficial.
Therefore, a gasoline engine is better for short distances and a diesel for longer distances, where its advantage is reflected in lower fuel consumption.
We probably don't need to write about whether diesel or gasoline is less consumed. If your only concern is fuel consumption, go for a diesel engine. Although modern gasoline turbo engines achieve beautiful consumption on paper, which is close to that of diesel engines, the reality is completely different.
In the same way, the consumption indicated by the manufacturer is just a scrap of paper, which has nothing to do with the real consumption during the car's operation. The truth is that modern petrol turbo engines can run even on very little fuel, but the driver must be careful and drive defensively.
If a person starts stepping on the neck with this engine, gasoline consumption can soar to double digits. With diesel engines, fuel consumption is not so sensitive to driving style. The same applies to high-volume naturally aspirated engines, albeit on a smaller scale, which are not so susceptible to consumption under heavy loads.
If you drive long distances and often on the highway, the diesel engine will pay off, at least in terms of lower consumption and, therefore, lower costs for the trip. In addition to the driving style, the car's weight determines fuel consumption. That is why diesel units, less susceptible to fuel consumption, are recommended for heavy vehicles.
If we compare the prices of diesel and petrol cars, we will see that diesel cars are more expensive than petrol cars. This, however, depends on the country in which they are sold. Sometimes this price difference is only a few hundred and several thousand.
In any case, this is also the case with used cars, where cars with diesel engines command a higher price than those with gasoline engines.
Reliability and maintenance:
In this case, the good old rule that what's not in the engine, can't go wrong, applies. The answer is clear if we compare an atmospheric gasoline engine with multipoint injection with a turbocharged diesel engine equipped with direct fuel injection. The gasoline engine is significantly simpler in design, which means that in most cases, the costs of service and maintenance will be lower than those of a diesel engine.
Related article - Naturally aspirated engine: What are its pros and cons?
However, the difference is not so great if we compare modern turbocharged gasoline engines equipped with direct injection with diesel engines. Simply put, all modern engines are complex; to top it off, they are riddled with electronics. The absence of a solid particle filter still works in favor of gasoline engines, which, as we all know, is not exactly the most reliable, but also not the cheapest car part.
After all, this means that, in most cases, a petrol engine's maintenance and service costs are less than a diesel engine's.
So is diesel or petrol better?
It's hard to say. Both are better and worse. Everything depends on what you will use the car for and what you expect from the car. The points mentioned above will help you decide between these two engines, so consider all the pros and cons and decide for yourself your favorite.
However, before we end this article, let's summarize the pros and cons of both engines.
Advantages and disadvantages of a diesel engine:
Diesel engines are structurally more complex than gasoline engines, but their performance is lower, mainly due to the combustion of a different fuel. When using the same technology and engine volume, the power of a petrol engine is always higher. However, the advantage of diesel engines is lower consumption and longer service life.
These engines are suitable for longer journeys and not short drives, as the time required to warm up the engine to operating temperature is much longer than it takes for a gasoline engine to warm up to proper operating temperature.
Advantages and disadvantages of a gasoline engine:
A gasoline engine has a simpler construction than a diesel engine, which means that its production is also less expensive, so cars equipped with a gasoline engine are usually cheaper than cars equipped with a diesel engine. In addition, the gasoline engine is significantly more powerful than the diesel engine (using the same technology).
These engines are also more suitable for short drives and the winter season. This is mainly because the time they take to reach operating temperature is much less than a diesel engine. The main disadvantage of petrol engines is their higher fuel consumption, which is more susceptible to driving style.
We hope you liked the article and learned whether diesel or petrol is better for you. If you have any comments or ideas, do not hesitate to write us in the comments and we will be happy to add valuable information to the article. Also, if you have an idea for a similar or other interesting article that you would like to read about, do not hesitate to contact us.