Why is a diesel engine more economical?
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Why is a diesel engine more economical?

Engines on such fuel have thermodynamics closest to the ideal Carnot cycle.

Diesel cars are most often bought by pragmatists. These are people who want to save not so much in the process of buying it, but in the process of its long-term operation - by reducing fuel costs. Other things being equal, diesel fuel always consumes less gasoline. But why?

Why is a diesel engine more economical?

If we take the same car with a gasoline and diesel engine with similar characteristics, the latter will always consume 2-3 liters, or even up to 5 (depending on volume and power) less fuel per 100 km. It is unlikely that anyone will doubt this (the price of the car itself and the cost of maintenance are not taken into account). This is a simple pattern.

What is the secret of a diesel engine? To understand the nuances, you need to turn to the design of diesel engines and the laws of thermodynamics. There are a number of nuances and aspects here. The diesel engine itself has a thermodynamic cycle different from the gasoline one, which is as close as possible to the ideal cycle of the French physicist and engineer Sadie Carnot. The efficiency of a diesel engine is usually much higher.

Why is a diesel engine more economical?

The ignition of the fuel in the cylinders of diesel engines is not due to the spark from the spark plugs, but due to compression. If for most gasoline engines the compression ratio is from 8,0 to 12,0, then for diesel engines it is from 12,0 to 16,0 and even higher. It follows from thermodynamics that the higher the compression ratio, the higher the efficiency. Cylinders do not compress the air-fuel mixture, but only air. Fuel injection occurs almost immediately after the piston passes top dead center - simultaneously with ignition.

In general, diesels do not have a throttle valve (although there are exceptions, especially recently). This significantly reduces the so-called intake air losses in the cylinders. This valve is also required for most gasoline engines. it consumes energy during operation. If the throttle valve is partially closed, additional resistance arises in the air supply system. Diesel engines usually don't have this problem. In addition, any modern diesel engine is inconceivable without a turbine that provides maximum torque at almost idle.

Why is a diesel engine more economical?

Finally, the efficiency of diesel engines is largely determined by the properties of the fuel itself. Initially, it has a higher combustion efficiency. Diesel fuel is denser than gasoline - on average, it gives 15% more energy when burned. Diesel, unlike gasoline (which requires an 11:1 to 18:1 ratio with air), burns in almost any ratio with air. The diesel engine injects as much fuel as is necessary to overcome the friction forces of the cylinder-piston group, the crankshaft and the oil pump. In practice, this leads to a decrease in fuel consumption at idle by 2-3 times compared to gasoline. This also explains the weak heating of diesel engines during operation. Diesel is always less thermally loaded, which means it has a clearly longer resource and more torque.

What does a diesel car owner actually get? On average, it is 30% more economical than its gasoline counterpart (in terms of fuel consumption). Combined with a variable geometry turbocharger and a common rail system, this produces truly impressive results. The diesel car accelerates well from low revs, consuming a minimum amount of fuel. This is what experts recommend to pragmatic people who love off-road travel. This type of engine is preferred in all-wheel drive crossovers and serious SUVs.

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