Fuel is taken from the fuel tank of the injection pump of the distribution type. In the high pressure fuel pump, the necessary pressure is created for the injection of diesel fuel and it is distributed among the cylinders in accordance with the order of their operation.
To reduce the content of harmful substances in the exhaust gas in vehicles with a diesel engine, special oxidation-type catalysts are used.
The high content of nitrogen oxides in the exhaust gases is reduced as a result of the operation of the exhaust gas recirculation system. The exhaust gas recirculation system helps to accelerate the ignition of the air-fuel mixture at lower temperatures and reduces the formation of nitrogen oxides (NOx). Exhaust gas reuse must be accurately metered to avoid increasing soot emissions.
In diesel engines, there are 3 different fuel injection methods: swirl or prechamber injection and direct injection.
When injected into the pre-chamber of the corresponding cylinder, the hot mixture immediately ignites. However, the volume of oxygen in the prechamber is sufficient to ignite only a portion of the injected fuel. The remaining, unburned part is blown into the combustion chamber by the overpressure that occurs during combustion. There, the fuel burns completely.
In swirl chamber injection, fuel enters a chamber separate from the main combustion chamber. The difference between swirl chambers and pre-injection chambers is a different design of the connecting channel between the swirl chamber and the cylinder. When compressed, an air vortex is formed in the swirl chamber, which ensures good mixing of the injected fuel with air, and the resulting mixture burns more quietly and more slowly.
Vehicles with 98 hp engine and direct injection
Fuel is injected by a high-pressure fuel pump directly into the combustion chambers of the cylinders, or rather into the grooves on the piston bottoms. The injection pump builds up pressure to 900 bar and then injects fuel in two stages.
First, a preliminary injection of a small amount of fuel is performed, which ensures better ignition of the main portion. Fuel injection is carried out by multi-string nozzles with two springs in the holder. This ensures a soft and quiet combustion of the air-fuel mixture, similar to what happens in engines with vortex combustion chambers. The amount of injected fuel is controlled by the electronic control unit. The advantages are low fuel consumption and high engine power.
The injection pump does not require maintenance. All moving parts of the pump are lubricated with diesel fuel. The pump is driven by the crankshaft via a toothed belt.
Vehicles with 102 hp engine and direct fuel injection
Fuel injection for these engines is carried out through the main fuel line.
Fuel filter heater
As the temperature decreases, the fluidity of diesel fuel decreases and waxing occurs.
Diesel fuel can become viscous, and its fluidity can be compared in this state to the viscosity of honey. As a result of thickening, the fuel filter becomes clogged. For this reason, diesel fuel manufacturers add additives to diesel fuel in winter to maintain the desired fluidity and ensure engine start at temperatures from -15°C to -22°C. However, these additives do not always ensure perfect engine operation.
To prevent clogging of the fuel filter during the cold season, an electric fuel pre-heater is installed in the filter holder.
Turbocharger
Diesel engine with 90 HP and 98 HP equipped with a turbocharger. In the turbocharger, two turbine wheels are installed on one shaft, which are located in housings separated from each other. The wheel drive is provided by exhaust gases. They bring the speed of the supercharger shaft to 120,000 rpm. And since the exhaust gas and supply air rotors sit on the same shaft, air is forced into the cylinders with the same frequency.
Due to the good filling ratio in existing engines, power gains of up to 100 percent can be achieved. The degree of this increase in power depends, among other things, on the boost pressure, which in a passenger car is between 0.4 and 1.0 bar (tire pressure, for example, is approximately 1.8 bar). If the boost pressure exceeds the value set by the manufacturer, the pressure reducing valve will open and the pressure will decrease.
Along with an increase in engine power, when using a turbocharger, torque is also increased, which is especially important from the point of view of achieving good engine elasticity. The prerequisite, of course, is a sufficiently high turbocharger shaft speed, which guarantees a decent filling ratio.
In contrast to an internal combustion engine, in a supercharged diesel power plant, it is not necessary to reduce the normal compression, which allows full use of the injected fuel even in the lower engine shaft speed range.
The turbocharger is an extremely precisely manufactured unit. Therefore, in case of repair, it is recommended to contact only a specialist. As a rule, in the event of a malfunction, the turbocharger is replaced completely.
The turbocharger is lubricated from the engine lubrication lines. To ensure sufficient lubrication of the turbocharger, the following rules must be observed:
- use only recommended engine oil;
- stale, old oil can lead to coking of the turbocharger. Therefore, the engine oil and oil filter should be changed strictly at the time specified in the maintenance plan;
- never operate the engine without an air filter. Even the smallest particles of dust can lead to failure and destruction of the turbocharger.
Preheating system and control unit
When starting a cold engine, even when the air is compressed, the self-ignition temperature of the air-fuel mixture is not reached. For this reason, especially for swirl chamber injection engines, the combustion chambers must be preheated. Preheating of the engine with direct fuel injection is only necessary at very low air temperatures.
For heating in the combustion chamber of each cylinder, a glow plug is installed, consisting of a body and an incandescent element pressed into it. As soon as voltage is applied to the incandescent element, it heats up to a temperature of over +850°C within a few seconds. Thus, the duration of preheating in rare cases exceeds 5 seconds. As soon as the preheat warning light on the instrument panel goes out, the engine can be started.
The duration of preheating and its automatic follow-up after starting the engine for approximately 20 seconds is carried out automatically by the heating control unit.
Preheating control unit A is mounted on the dividing wall of the engine compartment (see illustration 1.0).
1.0 Preheat control unit A is installed on the dividing wall of the engine compartment. The illustration shows the control unit for heating a car with a 64 hp engine.
The control unit has an air temperature sensor. Vehicle control unit with 98 hp engine. differs from that shown in the illustration only externally. It is also attached to the dividing wall. In addition to the heating process, the unit also controls the low pressure valve B of the air conditioner, if the car is equipped with it (see illustration 1.0). In this case, when the air conditioner is on, the idle speed is increased so that the engine does not stall. The same thing happens if, when starting the engine, sufficiently powerful consumers of the on-board electrical network are switched on, for example, a windshield heater. To avoid overloading the on-board network, the preheating control unit turns off the air conditioner for the time required for the glow plugs to heat up the combustion chambers.
In addition, the control unit switches EGR valve C on and off depending on engine load and engine temperature (see illustration 1.0).
When the coolant temperature is below + 29°C, the control unit supplies power to the valve on the injection pump, thereby ensuring an earlier start of fuel supply, which improves engine performance and exhaust gas composition. This valve is also actuated if the air pressure sensor, in the engine compartment on the relay box on the left side, registers an air pressure of less than 920 mbar. This contributes to better engine performance, for example in mountainous terrain. The regulation of fuel supply depending on atmospheric pressure and engine load is denoted by the abbreviation ALFB.
On vehicles with a turbocharger, the control unit performs more tasks. In this case, it receives data from the TDC sensor of the piston to cylinders 1, the vehicle speed sensor, and the accelerator lever position sensor on the injection pump. The start of injection is controlled by the needle stroke sensor on the injector of cylinder #4. As soon as this nozzle fires, the corresponding signal is sent to the control unit. The control unit recognizes failures in the power system and registers them. Subsequently, fault codes can be read out by contacting a RENAULT workshop in order to purposefully eliminate them.