Description of the common rail fuel system, Mazda RF-CDT, MZR-CD engine intake and exhaust systems
Exhaust system and emission control
The exhaust system is used to clean the cylinders of the combustion products of the air-fuel mixture. A number of elements and systems are installed in the exhaust system to reduce the content of toxic components in the exhaust gas. The toxicity reduction system of this engine includes:
– Exhaust Gas Recirculation and Throttle – Reduced NOx.
– Oxidizing agent – NOx reduction,, CH, CO.
– Diesel particulate filter “DPF” – reduction of soot particulate matter.
The engine has a forced crankcase ventilation system. The system is used to remove exhaust gases that burst from the combustion chamber into the crankcase. For this, a hose connecting to the intake manifold is connected to the cylinder head cover. Crankcase gases enter the intake manifold through the hose and then into the combustion chamber.
Oxidation Converter and Particle Filter (DPF)
The oxidizing agent and the particulate filter are combined in one housing. In this system, the process of reducing exhaust toxicity is divided into two stages.
At the first stage, the content of hydrocarbons CH and carbon monoxide CO decreases in the oxidizing converter. An exhaust gas temperature sensor is installed in front of the oxidizing converter, which helps to optimize the operation of the oxidizing converter and, in particular, to improve the process of reducing the CH content in the exhaust gases.
At the second stage, particulate capture is carried out with a particulate filter. A particulate filter is an element consisting of many cells (cells) in which carbon black is collected.
Carbon black particulate filter (DPF).
Due to the constant accumulation of particulate matter (soot) in the particulate filter, for its normal functioning, it is necessary to clean (burn) the particulate filter, otherwise the particulate filter may fail. A sign of clogging of the particulate filter may be a decrease in engine power, acceleration dynamics and increased back pressure.
The process of burning a particulate filter is the burning (oxidation) of soot at a temperature of about 600 ° C to non-toxic CO2. When starting the burning process, the injectors start injecting more fuel at the signal of the engine control unit (the main injection increases and additional injection is performed) and the throttle valve starts to work, as a result of which the exhaust gas temperature rises. Thus, when starting the process of burning the particulate filter, the exhaust gas temperature in front of the particulate filter is a key parameter for the successful process. To measure this temperature, an exhaust gas temperature sensor is installed in front of the particulate filter. An exhaust gas temperature sensor is also installed behind the particulate filter, monitoring the exhaust gas temperature after the particulate filter, thereby protecting the particulate filter from overheating.
The pressure sensor in the exhaust system (differential pressure) through the system of tubes and hoses detects the pressure drop after the gases pass the particulate filter. During engine operation, soot gradually builds up in the particulate filter and the pressure difference before and after the particulate filter increases. The signal from this sensor is used by the engine control unit to calculate the particulate filter contamination. Based on the readings of this sensor, the engine control unit decides whether to clean (burn) the particulate filter and lights the corresponding indicator.
The pressure sensor in the exhaust system (absolute pressure) monitors the pressure in front of the particulate filter and determines the composition (amount of soot) of the exhaust gases in front of the particulate filter.
1 – throttle, 2 – throttle body
To regulate the amount of air supplied to the engine, an electronic throttle valve is installed in the system, which helps to regulate the composition of the air-fuel mixture and the required amount of exhaust gas supplied to the intake through the recirculation system, which contributes to the completeness of fuel combustion and reduction of exhaust gas toxicity.
The presence of a throttle valve facilitates the process of burning the particulate filter by reducing the air supply during the burning process, as a result of which the temperature of the exhaust gases increases.
It also achieves smoothness and noise reduction when the engine is stopped after turning the ignition key to the “OFF” position, by closing the throttle and stopping the air supply to the engine.
The throttle is driven by an electric motor through a system of gears. The throttle opening is controlled by the engine control unit using the throttle position sensor.
In the event of a malfunction in the throttle control system, the throttle control is terminated and the throttle is fully opened by the return spring, which allows the vehicle to continue to move.
Exhaust gas recirculation (EGR)
The exhaust gas recirculation system is used to reduce the toxicity of exhaust gases by burning nitrogen oxides NOx in the combustion chamber.
|Exhaust Gas Cooler for Exhaust Gas Recirculation Cooler.||Exhaust gas recirculation valve.
1 – from the EGR cooler, 2 – to the intake manifold.
The system consists of an exhaust gas recirculation valve with a position sensor, two solenoid valves, a cooler and a pipe system. The exhaust gas recirculation system is controlled by the engine control unit using electromagnetic valves. The system has solenoid valve No. 1 (vacuum valve) and solenoid valve No. 2 (ventilation valve), using both solenoid valves, the engine control unit controls the opening of the exhaust gas recirculation system valve. By a signal from the control unit, the solenoid valves open and close, supplying either pressure from the vacuum pump (through the electromagnetic vacuum valve) or atmospheric pressure (through the ventilation valve associated with the atmosphere) to the valve diaphragm. By opening the valve of the exhaust gas recirculation system, the amount of exhaust gas transferred to the intake manifold and then to the combustion chamber is regulated. Afterburning of NO occurs in the combustion chamberx.
Elements of a system for changing the air flow rate at the VSC inlet.
The operation of the system for changing the intensity of the air flow at the intake VSC.
Air intake system
The air intake system serves to supply air to the engine cylinders. The system consists of a resonator (to reduce noise from the intake air), an air filter, a turbocharger, an actuator and dampers of the intake air flow rate (VSC) system, an intake manifold, tubes and hoses. To facilitate starting a cold engine, glow plugs are installed in the intake ports. A turbocharger with a bypass valve is installed in the system to improve cylinder filling. The turbocharger uses the energy of the exhaust gases to further compress the air at the inlet and supply it to the cylinders with high pressure and density, resulting in an increase in power, improving engine performance.
Intake Air Flow (VSC)
The system consists of an electro-pneumatic valve, an actuator and four shutters installed in the intake manifold and blocking one of the two inlet ports of each engine cylinder. The system serves to reduce the toxicity of exhaust gases at a low engine speed. At a low speed, according to the signal from the engine control unit, the electro-pneumatic valve opens the vacuum channel, as a result of which vacuum is applied to the VSC system drive. Under the influence of rarefaction, the drive closes one of the inlet ports of each cylinder with the help of dampers, as a result of which air is supplied to the open inlet port with greater intensity and turbulence occurs in the cylinder, which contributes to better fuel evaporation, distribution of the air-fuel mixture over the volume of the combustion chamber, as well as contributes to smoke reduction.
The RF-CDT engine has a common rail fuel injection system.
The main functions of the system are in the optimal and proper control of the diesel fuel injection process at the right time and in the required quantity, as well as with the necessary injection pressure, which is ensured by the use of an electronic control system. Such an organization of the injection process control provides a smooth and economical operation of the diesel engine. This system allows to reduce the content of soot particulate matter in exhaust gases and nitrogen oxides NOx.
The Common Rail battery fuel system includes: a low pressure stage, a high pressure stage and an electronic engine management system. The main elements of this system are electro-hydraulic nozzles, high pressure fuel pumps made by DENSO (HP3) (with fuel temperature sensor and fuel pressure control valve), fuel accumulator (with fuel pressure sensor and pressure reducing valve), sensors, valves, nozzle amplifier and electronic engine control unit.
Common Rail Battery System Diagram.
High pressure fuel pump. 1 – an eccentric shaft, 2 – a cam ring, 3 – a TNVD case, 4 – a plunger, 5 – a regul-
The low pressure stage consists of a fuel tank, a fuel filter and low pressure piping.
The high pressure stage in the common rail accumulator fuel system includes an injection pump, a fuel accumulator, nozzles, high pressure lines and fuel return lines. The high-pressure fuel pump is driven by a timing belt from the crankshaft and delivers fuel under the necessary pressure to the fuel accumulator. The injection pump includes a fuel priming pump (pumping fuel from the fuel tank to the plunger chamber), a fuel temperature sensor, a fuel pressure control valve, a cam shaft, and two plungers pumping fuel under high pressure into the fuel accumulator.
The amount of fuel supplied to the high-pressure plunger chamber is regulated by the control valve of the fuel priming pump. The fuel pressure control valve controls the amount of fuel supplied to the accumulator, thereby maintaining a constant pressure in the fuel accumulator. The valve is controlled by the engine control unit, at the signal of which the valve opens and excess fuel is supplied to the return line. The fuel temperature sensor includes a measuring resistor and is powered by a voltage of 5V. The resistance of the resistor varies depending on the temperature of the fuel, which in turn affects the output voltage (signal) sent by the sensor to the control unit. The control unit receives a signal from the sensor and determines the temperature of the fuel according to the algorithm embedded in its memory. Data received from the fuel temperature sensor is used to calculate the cyclic fuel supply.
Fuel from high-pressure fuel pump under high pressure enters the fuel accumulator, from where it is fed to the nozzles. The fuel accumulator maintains optimum pressure. If a certain pressure is exceeded, part of the fuel is drained through a pressure reducing valve (mounted on the fuel accumulator) to the fuel return line. A pressure sensor is also installed on the fuel accumulator.
1 – ports for connecting high pressure fuel pipes, 2 – pressure sensor-
fuel storage, 3 – gear-
tion valve, 4 – fuel accumulator.
1 – the electromagnetic valve, 2 – a rod,
3 – fuel exhaust channel, 4 – piston,
5 – needle, 6 – hydraulic chamber, 7 – fuel supply channel, 8 – to the fuel return line.
1 – from the fuel accumulator, 2 – electric-
solenoid valve, 3 – rod, 4 – piston, 5 – nozzle needle.
The system is equipped with nozzles with an electromagnetic control valve type “G2”. The nozzles are controlled by the engine control unit. Each nozzle consists of a spring-loaded piston, a needle, an electromagnetic valve and a hydraulic chamber. In a pressure chamber, the fuel is under pressure equal to the pressure in the fuel accumulator. When the nozzle is closed, the fuel presses on the spring-loaded piston, which, in turn, acts on the nozzle needle, preventing it from opening. When the electronic engine control unit issues a control start signal to the corresponding solenoid valve of the nozzle, the stem opens. The rod opens a channel connecting the hydraulic chamber to the fuel return line, as a result of which part of the fuel drains, and the pressure in the hydraulic chamber of the nozzle weakens. At the same time, the pressure of the fuel supplied to the nozzle needle overcomes the force of the piston spring and the needle opens, as a result of which the nozzle injects fuel into the cylinder.
The engine control unit controls the amount of fuel injected and the moment of injection. This fuel system can provide up to five sequential injections (multi-stage injection). Each nozzle is connected to the fuel return line..
An injector amplifier is installed in the circuit between the engine control unit and the nozzles. The main objective of the nozzle amplifier is to generate a high voltage (more than 50 V) from the battery voltage and transmit voltage to the nozzle. This is necessary to ensure a high injection rate and, thus, to obtain the possibility of organizing a multi-stage injection.
The amount of fuel injected by the nozzle is determined by the control signal constantly sent by the nozzle to the engine control unit.
On some models, depending on the installed engine control unit, a resistor is installed in front of the nozzle.
Using a resistor, the engine control unit corrects and eliminates the mismatch between the calculated and actual amount of fuel injected by the nozzle, which occurs due to the mechanical characteristics of the nozzle.
The fuel injection control is carried out by the engine control unit, based on the signals of a number of sensors, the engine control system, and also depending on the engine operating mode. The control unit controls the amount of fuel injected, the moment of injection and the number of injections per cycle in each cylinder separately.
The amount of injected fuel depends on the opening time of the nozzle needle, which is controlled by the control unit using the nozzle amplifier, depending on the accelerator pedal and the crankshaft speed. An adjustment is made to the estimated amount of fuel injected depending on the pressure and air temperature at the inlet and atmospheric pressure. Also, the control unit constantly adjusts the amount of fuel injected into each cylinder, depending on the change in the crankshaft speed, to reduce speed fluctuations. Corrective parameters are then entered into the memory of the engine control unit and used by him in the future. Correction parameters in the control unit memory are updated automatically depending on the vehicle mileage. It is also recommended that fuel cycle adjustments be made annually to improve performance..
The injection moment is calculated by the control unit based on the signals of various sensors, engine operation, crankshaft speed and the amount of fuel injected according to the algorithm recorded in the control unit memory. In the estimated fuel injection time, an adjustment is made depending on the intake air temperature, coolant temperature and atmospheric pressure.
The injection pressure directly depends on the pressure in the fuel accumulator and is controlled by the engine control unit based on the signal from the pressure sensor in the fuel accumulator.
Management of the number of fuel injections. 1 – sensor signal
crankshaft position, 2 – five injections, 3 – four
injection, 4 – three injections, 5 – two injections, 6 – one injection,
7 – pilot injection, 8 – post-injection, 9 – main injection.
The fuel pressure is regulated by the control unit depending on the speed of the crankshaft and the cyclic fuel supply using the fuel pressure control valve installed in the high-pressure fuel pump. Creating optimal fuel injection pressure helps reduce exhaust emissions.
The number of injections produced by the nozzle into the cylinder is controlled by the engine control unit depending on the vehicle’s driving conditions and serves to reduce vibration and exhaust gas toxicity. This rechargeable fuel system allows up to five injections per cylinder per cycle.
Several optimal fuel injection algorithms are programmed in the memory of the control unit for various conditions. So, at a low crankshaft speed and low load, four injections per cycle are performed to reduce the likelihood of detonation. At a high crankshaft speed and high load, only one injection per cycle is performed to improve power performance and reduce fuel consumption.
Additional control functions are used to improve performance to reduce emissions of harmful substances from exhaust gas and fuel consumption or are used to improve safety, comfort and ease of use..
Bushin Sergey, Legion-Avtodata
© 1999 – 2010 Legion Avtodata
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