9.1. The general data
The diesel engine is a piston engine with spontaneous ignition from compression. Its basic difference is preparation of a gas mixture of fuel with air in cylinders.
In the diesel engine fuel and air move separately. At first in the cylinder air is soaked up, then it is compressed and only after that in the end of a compression step fuel is injected.
Fuel spontaneous ignition is accompanied by sharp, spasmodic increase of pressure in the cylinder – it usually noisy, "rigid" work of the diesel engine speaks. In низкооборотных diesel engines of the big working volume which are used by lorries, this lack is shown to a lesser degree, and with it are reconciled. In diesel engines of cars of it try to get rid application of the vortical chamber, or the prechamber, – a small compartment of the chamber of combustion into which fuel is injected. There it ignites, partially mixes up with air then extends on the basic volume of the cylinder. This way reduces "rigidity" of work of the engine a little, but reduces its thermal efficiency and fuel profitability. For smoother ignition of fuel two-level injection and the difficult electronic scheme of management are used.
Prominent feature of diesel engines is presence in the fulfilled gases of firm particles – soot. For good burning of diesel fuel the quantity of air is required considerable, even superfluous.
Degree of compression of the diesel engine twice above, than petrol. High, not less than 14 (reaches 25), compression degree is necessary for increase in temperature of air in the cylinder to size, sufficient for fuel ignition. Usually in diesel engines compression degree makes 21–22 and is limited only прочностными to engine characteristics.
For fuel giving in diesel engines it is much more difficult than the device, than in petrol. Their complexity is defined first of all by that it is necessary to inject very small, all on some milligrammes, portions of fuel on Wednesday with a high pressure. For injection and fuel dispersion, and also for distribution of its particles on volume of the chamber of combustion atomizers serve. High degree of compression demands application of corresponding fuel pumps: pressure in an atomizer nozzle should reach several hundreds bar. It complicates all and is notable удорожает system of giving of fuel and, accordingly, the diesel engine.
Fuel from a fuel tank moves to atomizers the fuel pump of a high pressure.
For reduction of quantity of the harmful substances containing in fulfilled gases, on cars with diesel engines establish oxidising каталитический neutralizer. For this purpose the system рециркуляции the fulfilled gases is used also. Addition of the fulfilled gases in a working mix for decrease in limiting temperature of combustion allows to reduce in them emissions оксидов nitrogen (NOx).
Three ways of injection of diesel fuel in engine cylinders are known: through форкамеру, the vortical chamber and direct injection.
At injection of diesel fuel through форкамеру fuel is sprayed on it and instantly ignites. Because of insignificant quantity of oxygen in форкамере burns down only a fuel part, other part is superseded from форкамеры in the engine cylinder where burns down completely.
At fuel injection through the vortical chamber process of combustion of fuel occurs in the same way, as well as at fuel injection through форкамеру. Difference consists in the form and the sizes of the channel connecting the vortical chamber with the chamber of combustion. At fuel injection in the vortical chamber it mixes up with air is much better, and combustion process proceeds more smoothly.
At direct injection fuel arrives at once in the combustion chamber. The fuel pump submits fuel under pressure nearby 900 bar, and fuel injection is carried out in two stages.
Use of two-channel fuel atomizers gives the chance to make initial injection of an insignificant part of fuel therefore process of combustion of fuel improves, and process of combustion proceeds more smoothly. The quantity of injected fuel is regulated by an electronic control system of the engine on the basis of the information from gauges.
The stream of air arriving in the engine, in inlet channels twists on a spiral therefore combustion process in engine cylinders improves. Besides start-up of the cold engine is thus facilitated, and preliminary warming up of the engine is necessary for spending at air temperature more low–10 °С.
Before receipt in the fuel pump of a high pressure fuel passes through the fuel filter in which from it water which is necessary for merging periodically separates also.
The drive of the fuel pump is carried out by a gear belt. Its internal mobile details "are greased" with diesel fuel.
The car power supply system consists of a multisection fuel tank, pipelines, the fuel filter, топливоподкачивающего the pump, the fuel pump of a high pressure and atomizers.
The fuel tank is located under the bottom in a back part of the car. Ventilation of a fuel tank is carried out through the closed system of removal of air. At ventilation of pair fuel from a tank are caught by the canister with the activated coal – an adsorber.
Do not suppose hit of diesel fuel on hoses of system of cooling. Hoses which long time influenced diesel fuel, it is necessary to replace.
The power supply system of the diesel engine is especially sensitive to pollution, therefore at work on system observe the maximum cleanliness. Before separation топливопроводов carefully clear them of a dirt. At removal of elements of system close open places безворсовой a fabric.
Do not use compressed air for clearing of elements of the system established on the engine.
At check of work of atomizers never substitute hands or any part of a body under the stream of fuel leaving an atomizer. Fuel leaves an atomizer under a high pressure and can get inside through a skin.
For protection of eyes against hit in them of fuel use points. At fuel hit on a skin wash out its considerable quantity of water.
Establish only pure elements of the power supply system.
Spare details take from packing directly ahead of their installation.