What is the Difference Between a Gasoline and Diesel Engine

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For decades, motorists have been arguing about which combustion engine is better – diesel or gasoline. And although there is nothing wrong with disputes, because, as you know, truth is born in them, it is paradoxical that very often the participants in the discussion do not really understand the objective advantages and disadvantages of one or another type of internal combustion engine. In order to remedy this situation, today we will analyze the design features and the mechanics of each type of engine, forming a complete list of pros and cons of both a diesel engine and a gasoline engine. This will expand the horizons of the motorist, and will allow you to choose the optimal engine for a specific purpose.

  • ⚠️ Important: both gasoline and diesel power units are internal combustion engines – they use the energy of fuel combustion in the working chamber, converting it into mechanical work of the engine.

Before studying the differences between diesel and gasoline engines, it is worth understanding what components an internal combustion engine consists of. The fact is that the “internal stuffing” of the power plant can be conditionally divided into two most important components – the gas distribution mechanism (GRM) and the crank mechanism (KShM), which play a major role in the combustion process. Actually, the KShM is necessary in order to convert the energy from the combustion of fuel into rotational-mechanical energy, which “turns” the wheels of the car, and the timing belt is responsible for supplying the mixture to the working chambers for further combustion.

How does a gasoline engine work

The mechanics of the operation of a gasoline internal combustion engine is actually extremely simple and is divided into four strokes (two-stroke engines are rarely used in cars):

  1. Inlet. When the piston reaches the top dead center of the working chamber, the “cams” of the camshaft of the gas distribution mechanism (timing) open the intake valves, filling the working chamber with a fuel-air mixture (air and gasoline) until the piston reaches the bottom dead center – at this moment the inlet valve closes.
  2. Compression. In the second stroke, the piston moves from the bottom dead center to the top, compressing the fuel-air mixture – because of this, its temperature rises noticeably.
  3. Working stroke. At the end of the previous stroke, when the piston has almost reached the top dead center, the compressed and heated (up to 500 ° C) fuel-air mixture is ignited by a spark from the spark plug. The process of fuel combustion begins, during which the combustible mixture reaches a temperature of 2200 ° C, and the pressure in the working chamber rises on average three times. Under the pressure of expanding gases, the piston moves from top dead center to bottom, spinning the crankshaft of the KShM with the help of a connecting rod. It is at this cycle that the transformation of thermal energy into rotational mechanical energy occurs.
  4. Release. On the fourth stroke, the gas distribution mechanism opens the exhaust valve, and the piston, moving from the bottom dead center to the top, squeezes out the exhaust gases formed there from the working chamber, after which the exhaust valve closes – the full cycle of the internal combustion engine is completed.

That is, fuel is supplied to the working chamber of the cylinder, which is compressed and ignited by a spark (this is a very important point), after which the piston, by the action of gases, pushes the connecting rod, transferring rotation to the crankshaft, and that, relatively speaking, to the wheels of the car.

How does a diesel engine work

Despite the common misconception, the process of operation of a diesel engine is (almost) no different from its gasoline counterpart – there are also four strokes, for which the crankshaft makes two revolutions, and the strokes themselves are absolutely the same. But, of course, there are nuances:

  1. Inlet. At the first stroke of the engine operation, air (without the fuel mixture) enters the cylinder working chamber through the intake valve, while the piston moves from top dead center to bottom, conventionally “sucking” air, after which the valve closes.
  2. Compression. In the second stroke, the piston moves from the bottom dead center to the top, compressing the resulting air, thereby significantly increasing its temperature (up to 500 ° C) and the total pressure in the working combustion chamber.
  3. Working stroke. At the end of the previous stroke, when the piston has almost reached its top dead center, diesel fuel is injected into the working chamber through the nozzle, which ignites from interaction with compressed air of increased temperature. During this process, gases are formed in the chamber, which, in fact, squeeze the piston back from top dead center to bottom, transferring rotation to the crankshaft due to the connecting rod. This, as in the gasoline counterpart, is the main driving force of the engine.
  4. Release. At this stage of the engine operation, the exhaust valve opens, and the piston, returning to the top dead center, pushes the exhaust gases out of the combustion chamber, after which the exhaust valve closes, completing the full cycle of the internal combustion engine.

In short, air is supplied into the combustion chamber, which is compressed with an increase in temperature, after which diesel fuel is injected into this compressed air, which ignites from an elevated temperature (a key difference from a gasoline engine), and the piston, under the influence of gases, pushes the connecting rod, converting the most energy of combustion of fuel into mechanical energy of rotation of the crankshaft.

Spark and compressed air: subtotal

It turns out that there are only two differences in the operation of gasoline and diesel engines:

  1. at the injection stage, the gasoline engine pumps air into the working chamber together with fuel, while the diesel engine at the first stroke only pumps air;
  2. in a gasoline engine, the mixture is ignited with the help of a spark from a spark plug, and in a diesel power plant, ignition occurs from the injection of diesel fuel into the air heated by compression.

Advantages and Disadvantages: Objective Facts

Now that we’ve figured out how each motor works, let’s explore the pros and cons of each option.

Efficiency and consumption

Despite the fact that gasoline engines usually boast more power, the efficiency of diesel fuel is noticeably higher – as much as 40% compared to its direct competitor. Moreover, the fuel consumption of a diesel engine is, on average, 20% less – it is precisely because of the diesel engine (if only the fuel consumption per 100 km of travel is taken into account) that it is cheaper.

Service costs

Although the cost of diesel fuel consumed while driving is lower than that of gasoline, the maintenance and upkeep costs of the diesel engine itself are higher. The fact is that the diesel engine needs to be serviced more often – to change filters, oils, check the necessary compression in the cylinders. And the repair of “diesel”, given the more complex design, usually comes out more expensive. On the other hand, even taking into account more expensive maintenance, in the long term, drivers who travel from 15-20 thousand kilometers per year, due to lower fuel consumption, still save a little compared to gasoline counterparts.

Fuel quality and temperature

There are subtleties of operation that many motorists do not even know about. Firstly, a diesel engine is much more whimsical in terms of fuel quality than a gasoline engine. Accordingly, if a gasoline internal combustion engine can be refueled anywhere and practically anything (bad gasoline leads to increased consumption, but minimal damage to engine components), then it is better to refuel a diesel analogue at proven gas stations. Secondly, diesel is not good at low temperatures – at -15-20 ° C, the usual fuel mixture thickens and does not pass through the fuel filter. This means that the fuel must either be heated or special grades of diesel must be used.

Thirdly, it will not work to warm up quickly in a diesel car, since it takes much longer to warm up – heat will enter the interior at least 10 minutes after starting. Because of this, diesel engines are usually not purchased in regions with low temperatures. On the other hand, a diesel engine has a noticeable plus – this engine uses electricity only for starting, so diesel engines are often installed on SUVs so as not to be afraid of water.

Noise and exhaust

Diesel engines are always noisier and emit more vibration even at idle than gasoline counterparts – this is due to the fact that the combustion of fuel in the working chamber occurs under high pressure. And since manufacturers rarely equip diesel cars with additional noise insulation, the difference between the two vehicle models on diesel and gasoline is usually audible even at a great distance. On the other hand, the diesel engine has less exhaust gases, so it is easier for such cars to obtain the Euro-4 and higher certification, while gasoline cars have to be equipped with additional filters to pass the certification.

No better and no worse – everything is situational

This is not to say that one type of motor is better, and the other is worse – this is not entirely correct. They are just created for different purposes and tasks. For example, if you drive 15-20 thousand kilometers a year, then a diesel engine will save on fuel, but you need to take into account that in cold regions problems can arise at low temperatures, and the fuel must be of high quality. For a city, a small mileage per year and low temperatures, a gasoline engine will be more convenient and comfortable, and you will also use a service to replace consumables less often. It is enough to define the task that you set for the car, and based on this, choose the type of engine.

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