Gasoline vs Diesel Engines: Which is Better? There are several factors to consider when purchasing a new vehicle, one of which is deciding the type of engine, if it is a gasoline or diesel engine vehicle you need.
Both gas and diesel engines are internal combustion engines that convert fuel to energy.
Diesel and gasoline engines perform the same functions and people sometimes mistakenly assume they are the same. However, there are some differences in how these engines operate which will be discussed in this article.
Choosing the Right Type of Engine
Diesel engines perform better, especially for those that drive on the highway often and put more miles on it. This is because diesel fuel is loaded with more energy, which makes it more economical.
Vehicles with a diesel engine have more torque and consume less fuel resulting in good fuel economy. For those who engage in city driving, gas engines are reliable.
Knowing and comparing the differences, advantages, and disadvantages of both diesel and gasoline engines will help you to know the engine that is best suited for your daily activities.
Diesel engines have better fuel economy and efficiency because diesel has high energy density which implies that a small quantity can produce a high volume of work as compared to very volatile gasoline.
Heavy-duty vehicles and equipment, such as power generators, trucks, and cruise ships use diesel engines because of their high torque and ability to do more work. Diesel engines are suitable for people who drive many highway miles and are also suitable for towing and hauling because of their high torque.
Gas engines on the flip side have high dynamics and power. They are very fast and flexible and make road movement easy.
Choosing the right type of engine requires you to consider the reason you need the vehicle and the volume of work the vehicle is expected to perform as well as your financial capacity.
A gasoline engine is not a bad choice if you do not engage in long miles of driving or need a vehicle to convey heavy loads or perform more demanding tasks.
Since diesel engines are built robustly, the casting and cylinders are thicker than that of gasoline engines, they can perform more strenuous activities without the parts wearing out easily.
Vehicles powered by gasoline engines are not so expensive as compared to the diesel variant. So, if you need something more affordable, you can always opt for gasoline-powered vehicles.
How Diesel Engine Works
A diesel engine works differently from a gasoline engine. Although both work on the four-stroke cycle, there are differences in how power output is regulated, how fuel is ignited, etc.
The diesel engine is an internal combustion engine just like the gasoline engine. It uses a series of combustions to power the vehicle and this combustion occurs differently from gasoline engines. They have no spark plug to ignite fuel, rather it creates combustion by absorbing oxygen-rich air and compressing it until it combusts.
A diesel engine has a crankshaft, cylinder, rods, and pistons, which transfer fuel energy from a linear to a rotary motion. It injects fuel directly into the cylinder during the power stroke, which then combusts as a result of high cylinder pressure.
Unlike gasoline engines, diesel engines introduce only air into the combustion chamber and are constructed typically with compression ratios in the range of 14:1 – 22:1.
Below is the four-stroke process in a diesel engine:
Intake valves open up to let in air as the piston goes down.
During the process, the piston travels from the top dead center in the cylinder bore to the bottom dead center, creating a low pressure in the cylinder while oxygen-rich air is drawn in through the open intake valves.
The piston returns from the bottom dead center in the cylinder bore to the top dead center compressing a large volume of oxygen and heating it in preparation for combustion.
As the piston is returning to the top dead center in the cylinder block, combustion occurs as a result of an induced spark.
Power stroke (combustion)
When the piston is at the top dead center of the cylinder block, it ignites when fuel is injected.
It is the pressure created from the combustion process that pushes the piston downward where the power of combustion is transferred to the crankshaft.
At this stage, the piston moves from the bottom to the top of the cylinder, and exhaust gases are released through the exhaust valves in the course of this. The exhaust gas escapes to the emissions or aftercare. It is then released into the atmosphere.
One feature that stands out about the diesel engines and that’s their efficiency. By compressing air, diesel engines are not faced with ignition problems like spark-ignition engines/gasoline engines.
How Gasoline Engine Works
Gasoline engines also known as spark-ignition engines are popularly used as the source of energy for cars. They are used in many parts of the world in vehicles people drive daily.
Gasoline engines utilizes the internal combustion process just like a diesel engine. It mixes fuel and air in the combustion system and ignites it to generate energy. The energy released allows your vehicle to perform its functions.
A gasoline engine has high engine speed and power while maintenance is quite easy. The gasoline engine, just like its diesel counterpart, makes use of the four-stroke combustion process as discussed earlier. Here, the mixture of air and gas is absorbed by the cylinder. The mixture is further compressed by the pistons and ignited by the spark plug to create combustion.
Differences between Diesel and Gasoline Engines
There are several areas of differences between diesel and gasoline engines and they include;
Differences in power output
Diesel engines tend to have higher torque and less horsepower while on the contrary, the gasoline engines have higher horsepower and less torque.
Torque is the twisting force that communicates with the engine’s rotational force and the measurement of the twisting force on the engine’s driveline while horsepower is a measurement of power.
Big trucks and other heavy-duty vehicles usually have diesel engines because of the high torque which helps to move the vehicle with heavy loads. Whereas sports cars make use of gasoline engines because of the higher horsepower gasoline engine offers.
Diesel engines appears to be more efficient than gasoline engines. They have more thermal efficiency than gasoline engines because they convert more heat to mechanical energy and waste less of it.
Diesel engines offer better fuel economy compared to gasoline engines. Although diesel fuel is more expensive, the cost is quite reasonable when you consider fuel economy and workload.
Diesel fuel is more energy-dense. It has more power than gasoline in the same volume of fuel and also being able to do more work with a small quantity of diesel, hence, more fuel economical.
Both diesel and gasoline engines make use of internal combustion and a series of explosions to convert fuel to mechanical energy which is required to move a vehicle.
The difference lies in how these explosions occur. In gasoline engines, spark plugs ignite the mixture of air and fuel compressed by pistons while in diesel engines, the air is compressed to make it very hot then fuel ignites when it gets in contact with this hot air.
In terms of reliability, the diesel engine can work for many hours and miles without major servicing which is not the same for gasoline engines.
Diesel engines have fewer parts that can malfunction but high repair bills if they eventually go bad.
Diesel engines run at lower RPM (revolutions per minute) and as a result of this, the engine can last longer because of reduced wear and tear.
Gasoline and diesel engines make use of different fuels because both engines operate differently.
Diesel fuel is thicker than gasoline which explains the reason diesel dries up slower than gasoline and this thickness makes it more energy-dense.
As a result of the features it possesses, diesel fuel has better fuel economy. Gasoline fuel on the other hand is cheaper than diesel fuel but a small quantity of diesel can do the same work a larger quantity of gasoline will do.
Injection of fuel
Both engines inject fuel in different ways. For the diesel engine, fuel is injected directly into the cylinder.
Fuel injection is a crucial process in the functioning of an engine. Diesel injectors are used to inject fuel into the engine and to deliver the appropriate amount of fuel, the injector must be able to withstand high temperatures. Whereas in gasoline engines, fuel injection can occur in two ways: through a carburetor or port injection system.
The carburetor produces an air and fuel mixture before sending it to the cylinder to compress while the port injection system injects air into fuel before the intake stroke.
Diesel vs Gasoline Engines: Similarities
The main similarity between diesel and gasoline engines is that both engines utilize internal combustion to convert chemical energy to mechanical energy.
Both engines work with heat and pressure to drive the internal mechanical structure that transfers power to the wheels and axle. The mechanical energy created as a result of the combustion moves pistons in an upward and downward direction inside the cylinder which creates a rotary motion that helps to move vehicles forward.
Both engines compress air and fuel mixture in the cylinder before it is combusted and it makes the crankshaft turn. The crankshaft is responsible for powering the wheels of the vehicle.
Another similarity is that both gasoline and diesel engines make use of the four-stroke combustion cycle: intake stroke -> compression stroke -> power/combustion stroke -> exhaust stroke.
The combustion cycle is a series of short explosions that convert fuel into mechanical energy that helps the vehicle move.
In each of these processes, different activities occur inside the cylinder to release energy.
Both gasoline and diesel engines make use of fuel to power the internal combustion engine. The fuel used to power these engines comes from the same source – crude oil and both diesel and gasoline are known as hydrocarbon liquid fuels.
Without fuel, combustion cannot take place in both engines. Gasoline engines make use of gasoline/petrol while diesel engines make use of diesel fuel. However, diesel fuel tends to be more energy-dense as compared to gasoline.
Advantages of Gasoline Engines
Low maintenance cost
Due to less complexity, gasoline engines are easier and cheaper to maintain. This is one feature that makes people consider gasoline engines.
One can easily find a repair shop and the parts are readily available, unlike its diesel counterpart which you might likely abandon your vehicle for a while if it goes extremely bad.
When buying cars powered by gasoline engines, there is always a wide range of choices and options available for you to pick from, unlike diesel-powered engines where you will only have a handful of options to pick from, be it a car or truck.
Low cost and availability of fuel
Filling up your tank if you are using a gasoline engine is inexpensive as compared to diesel fuel which is about 35% more expensive.
Also, fuel stations are available almost everywhere, making it convenient to use vehicles powered by gasoline engines.
Gasoline engines release lesser emissions into the atmosphere compared to diesel engines.
Both gas and diesel engines have emissions but one is worse. For instance, a gallon of gasoline in an engine produces about 19.59 lbs of CO2 while the same quantity of diesel produces 22.44 lbs of carbon dioxide (CO2).
Also, the exhaust from gasoline engines is usually cleaner as a result of fewer impurities present in the fuel. They are more eco-friendly than their diesel counterpart.
High dynamics and power
Vehicles that are powered by gasoline engines have high dynamics, easy acceleration, and power.
They have high horsepower which gives them the ability to do more work at a faster rate. They are very responsive, not weighty, and very fast when compared to diesel engines.
As a result of higher horsepower in gasoline engines, vehicles powered by this type of engine are very fast. This is why sports cars are equipped with this type of engine.
Disadvantages of Gasoline Engine
Lower thermal and engine efficiency
As compared to diesel engines, gasoline engines have lower thermal efficiency. These engines tend to consume 20% to 30% more fuel than a diesel engine.
Also, gasoline fuel does not have a high energy density as diesel, as such they get used up quickly and do not last long in the tank.
Shorter life expectancy
This is another major disadvantage of gasoline engines.
Gasoline engines might begin to show some signs of wear and tear or other signs of failure when they drive up to 150,000 to 170,000 miles which are not the same as diesel engines. Diesel engines have a longer life span because of their robust nature and low RPM.
Since gasoline engines are capable of operating at very high speeds, they tend to go bad fast.
Lower resale value
Fuel efficiency, reliability, life span, and engine capacity of gasoline engines decline over time, directly influencing their resale value.
Diesel engines are better valued if you want to resell them.
Due to the existence of several components in the gasoline engine, coupled with its short lifespan, gasoline engines are less reliable. For instance, spark plugs might get contaminated by soot and begin to display signs of failure.
Gasoline engines have more components that may go bad quickly as compared to diesel engines, this implies that they require servicing more often.
Advantages of Diesel Engines
High thermal efficiency
One major advantage of a diesel engine is its high thermal efficiency. This is how efficiently diesel engines convert heat energy from combustion to usable mechanical energy.
The diesel engine has a higher compression ratio than gasoline engines. It can employ a compression ratio of 16:1 to 22:1 contrary to the 9:1 to 12:1 range of gasoline engines.
Higher thermal efficiency leads to a high rate of gas expansion during the power stroke that converts a huge amount of heat energy to mechanical energy used for work. Diesel engines have a great work output, which is the reason they are used in different equipment and vehicles ranging from trucks to cruise ships and power generators.
This is another significant advantage of diesel engines. Diesel engines have a longer life cycle and can drive as far as 200,000 to 300,000 and even 500,000 miles without being worn out.
If some components begin to wear out, they can be changed without having to replace the entire engine. Also, the cylinder in the diesel engine is built thicker, and castings are thicker too making it robust and tending to last longer.
Better fuel economy
Diesel engines have better mileage as compared to gasoline engines. This is because of the high efficiency of diesel fuel. Diesel fuel is energy-dense and a small amount can produce a high volume of work.
Diesel contains 10% more potential energy per volumetric unit than gasoline. A gallon of diesel contains 13% more of the energy contained in a gallon of gasoline which implies that diesel provides a better fuel economy because a gallon of diesel will produce more usable mechanical energy than a gallon of gasoline.
Low RPM and High Torque
Diesel engines have lower revolutions per minute but very high torque as compared to gasoline engines which are one reason diesel engines don’t wear quickly.
Due to less wear and tear, the engine life expectancy is longer. The high torque diesel engine possesses gives it the ability to handle heavy loads which is why it is used in heavy equipment, trucks, and for hauling and towing.
High resale value
Diesel engines have a higher resale value as compared to gasoline engines. Since they don’t wear out quickly, they can still be as good as new when you are ready to resale.
Diesel engines wear half the rate of gasoline engines, placing them on a very high resale value.
Disadvantages of diesel engine
Despite their magnificent advantages, diesel engines are not without disadvantages.
Some of those disadvantages are:
Cold or hard starting is very common in diesel engines. Since they don’t have spark plugs or electric wiring to ignite them, they have difficulties starting in cold temperatures.
When the air in the engine is not hot enough, it won’t be able to ignite the fuel making it difficult to start the vehicle. In this situation, you will need heating elements and block heaters to counter the problem.
High cost of diesel fuel
The cost of diesel fuel is very high which is one reason why diesel engines/vehicles are yet to get a complete global acceptance.
A gallon of diesel fuel is twice more expensive as gasoline.
High cost of purchase and maintenance
The cost of acquiring a vehicle with a diesel engine is very high as compared to the gasoline variant.
The parts of diesel engines are very sophisticated and are designed to perform more tasks and handle more strenuous activities. If any of these goes bad, it is quite expensive to replace.
Diesel engines tend to be noisier than gasoline engines.
Although improved and modern diesel engines are not so noisy, if you pay close attention to both engines, you will still notice that diesel engines are noisier than gasoline engines.
More harmful emissions
Even with the advances and improvements in the manufacturing of diesel engines, they still release harmful emissions like nitrous oxide (NOx) and carbon dioxide emissions as compared to the rate released by gasoline engines because their combustion is very hot and runs lean.
Diesel vs Gasoline Engine: Which is better?
There is no clear answer to this, rather you need to look out for the things you will need in your vehicle, your driving habits, what purpose it will serve, and the advantages/disadvantages of both diesel and gasoline engines.
Knowing the differences as well as the pros and cons of each engine will help you decide which one is suitable for you.
After weighing these factors and features, you can now decide which is better or right for you. Diesel engines are said to be thermal efficient which implies that they can do more work because they possess more torque.
Little wonder they are used in large equipment and vehicles like trucks, power generators, and ships. Also, they have increased fuel efficiency and economy meaning that it uses little fuel while doing more work.
A small amount of fuel can produce a large volume of work. This is because diesel fuel is thicker and more energy-dense when compared to gasoline. Diesel engines have a longer life span and can be driven for longer miles without servicing because they function at low RPM and because of this, there is less wear and tear.
Gasoline engines on the other hand have high dynamics and power, they accelerate easily, move faster, and are very suitable for people that engage in city driving and not long miles.
Gasoline engines have higher horsepower which gives them the ability to do more work at a faster rate. Due to their agility, gasoline engines are very suitable for sports vehicles. Also, cars powered by gasoline engines are cheaper to acquire and easier to maintain.
Frequently Asked Questions About Diesel vs Gasoline Engines
Do diesel engines burn fuel while idling?
Yes! Over 1 to 4 gallons of fuel can be burnt if you leave your engine idling for up to an hour. The quantity of fuel consumed depends on the size of the engine and how old the engine is. Idling has to do with running a vehicle’s engine when it is not moving. Idling vehicles consume a lot of fuel which directly affects how often you need to refuel and how much you spend on refueling. Both gasoline and diesel engines burn gas while idling and in fact, diesel engines burn more gas when the vehicle is idling.
Why do diesel engines have less horsepower?
Horsepower is the power an engine produces and is usually gauged by the rate it takes to do work. Diesel engines have lower RPM as compared to gasoline engines and because of this, they are not as fast as gasoline engines and do less work per minute as compared to gasoline engines which makes them operate on less horsepower and more torque.
Do gas or diesel engines last longer?
In terms of lifespan, diesel engines tend to last longer than gasoline engines. Since diesel engines operate at low RPM, they do not wear out fast. Also, the components of diesel engines are very durable. The cylinders and casting are built thicker than that of gasoline engines giving them the tendency to last longer.