PRINCIPLE OF EXHAUST GAS TURBOCHARGER
In a turbocharged engine, the exhaust gas which would normally be wasted is used to drive a turbine.
The turbine in turn drives a compressor, which draws in air and compresses it, and supplies it at a higher pressure to the engine.
Due to higher air availability and by supplying more fuel, engine power output can be increased.
Higher air availability helps in better combustion, thus leading to reduced fuel consumption and less emission.
As a result, turbochargers contribute significantly to the protection of the environment and better utilization of energy resources.
Turbocharger (TC) primarily comprises of a compressor section and a turbine section.
The turbine and compressor wheels are mounted on a common shaft, hence they rotate as a single unit.
This sub-assembly is known as the rotor assembly. The rotor assembly is supported by journals placed inside the central housing.
The turbine section consists of the turbine wheel and turbine housing.
The pressure energy available in the exhaust gases is converted into Kinetic energy by the turbine housing and is used for rotating the turbine wheel.
The compressor consists of the compressor wheel and compressor housing. The compressor wheel draws in air axially and delivers it radially at a higher velocity.
The compressor housing converts higher velocity air into higher pressure.
The central housing consists of all the supporting & sealing components required for the rotor assembly.
Journals & thrust plate for supporting rotor assy, and the lubricating oil passages for oil supply & drain. Piston rings for sealing.
For reasons of improved TC response, a turbine housing with a smaller cross-sectional area is chosen such that sufficient boost pressure is available at lower engine speeds.
Part of the exhaust gas is bypassed once the required boost pressure is reached.
This is achieved by opening a valve, operated by a spring-loaded diaphragm (actuator assembly) with the help of boost pressure available in the compressor housing or with the help of an external vacuum supply.
The turbine flow cross-section varies by the engine ECU demand by variable guide vanes placed in the exhaust gas flow area of the turbine housing.
As a result of continuous turbine cross section adjustment to the engine airflow Actuator assembly / Waste gate requirements, high engine torque at low speeds and adequate control strategy ensure a significant improvement in the dynamic performance of a vehicle.
Guide vane control is mostly electronic through a vacuum-regulated actuator.
Regulated two-stage turbocharger (R2S).
This system uses one low-pressure turbocharger and one high-pressure turbocharger i.e. two turbochargers for one engine.
This technology helps in increasing the engine’s specific power output (power-to-weight ratio) and also helps in downsizing the engine while meeting the performance requirements.
The engine manufacturer’s recommendations for operation and maintenance shall be authoritative for the operation of a turbocharged engine.
Special attention should be paid to the following:
Use only the correct part number, i.e., TC approved by the engine
manufacturer.
Check the engine exhaust manifold and its connections to the TC for cracks and distortion and are free from foreign material, i.e., core sand particles, loose nuts, bolts, washers, etc.
The exhaust systems should be checked for blockage (damaged pipes, faulty exhaust brake, choked silencer/catalytic converter etc.), leakages, and their proper alignment and support.
Clean the TC compressor outlet to the engine intake manifold connecting pipes, hoses and intercooler for residual engine oil, before the new TC is fitted.
Check the connections i.e. pipes for wear, damage, correct alignment, and hoses for cracks/ageing. Check the intercooler for leaks and blockages.
Check the hose clips for their proper functioning. Replace with recommended clips wherever necessary.
Check air cleaner, filter elements, and its connecting pipes and hoses to the TC are free from foreign material.
Air filter elements should be cleaned/replaced as recommended by the engine manufacturer.
Oil inlet and drain pipes, and connections to the TC, should be examined for carbon deposits, cracks, distortion, etc.
Pipes should be thoroughly cleaned before fitment. If found damaged, it should be replaced.
Ensure that the recommended size of the oil inlet pipe and banjo bolts are used.
During replacement, care should be taken for proper routing and fitment to avoid excessive stress on the connection.
Replace the engine oil and oil filter, if necessary (adhere to the engine manufacturer’s recommendation for correct grade and change periodicity)
Disconnect the TC actuator operating switch/hose (for VTG TCs) during the first starting.
Connect the TC actuator operating switch/hose (for VTG TCs).
With the engine in running condition, check the oil line, air and gas connections for leakage and their proper functioning.
Check oil inlet and return line connection for leakages.
Ensure that the air cleaner to TC connections are intact. Check air leakages at compressor outlet to inlet manifold.
Check exhaust gas leakage at the exhaust manifold and the turbine housing joints.
The most common reason for NOISE complaint is a small leakage of exhaust gas or compressed air.
CAUTION: Stay away from running the turbocharger (at engine higher RPM)
Note: Follow the same inspection procedure for the turbine side also.
Check the TC actuator assembly for its proper functioning i.e. check for damages, tampering, and loose or open connections.
The normal working condition:
With the engine switched off, TC actuator will be in OPEN condition i.e. Actuator control rod length will be maximum.
When the engine is switched-on (while the engine is in running condition), TC actuator control rod will be in a closed condition, i.e., the actuator control rod length will be minimum.
During the engine operation, the TC actuator control rod moves freely without restriction.
Symptoms: Vehicle speed is not O.K, Check Engine light is ON.
Diagnosis on the Vehicle: Connect the engine diagnostic and check for fault code (Ex.: Engine airflow deviation – Not O.K)
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