The secondary air injection system of gasoline engines ensures a reduced emission of pollutants in the warm-up phase when starting the engine. During this time, the engine requires a mixture with fuel surplus until reaching the operating temperature, with the result that some of the fuel leaves the combustion chamber unburned. Since the lambda control and the catalytic converter don’t have the time to warm up during the cold start phase, the harmful hydrocarbons and carbon monoxides can be released into the environment without aftertreatment. For this purpose, the secondary air system is installed behind the outlet valves.
Over time, internal combustion engines may lose their performance due to a variety of reasons. Mainly because of the aging of the engine, the burning process no longer runs too frictionless and ‘smoothly’ as at the beginning. For this purpose, the air and fuel supply, as well as the compression and ignition play an important role. Continue reading “Power loss of internal combustion engines – Problems & How to Repair”
A turbo-compound engine uses the exhaust gases through a downstream turbine. This can be installed in addition to a turbocharger.
While the first exhaust gas turbocharger provides more boost pressure in the combustion chamber due to the exhaust gas energy and thus higher engine power, the second turbocharger converts the remaining energy into movement power. The generated energy is passed on to the crankshaft via a mechanical or hydraulic transmission.
The overall complexity of a turbo-compound system and especially for road vehicles quite low saving effect has prevented widespread introduction of the turbo-compound engine.
The steering is generally a part of the chassis, and responsible for the directional control of the vehicle. It allows the driver to influence the direction of travel by turning the wheels of the front steering axle in the desired direction.
Basics OF THE STEERING
In the basic principle, the movement of the steering wheel is transmitted via the steering column to the steering gear, which transmits the movement in direct or indirect form to the tie rods.
The exhaust system receives the exhaust gases escaping from the exhaust valves of the cylinders through the exhaust manifold. These are attenuated in their noise generation after they have been cleaned in the catalyst, and discharged into the environment at a suitable part of the vehicle. The entire system is connected to the underside of the vehicle with the vehicle floor.
In a diesel or gasoline engine with direct fuel injection, the fuel is injected through a nozzle with up to 200 bar directly into the combustion chamber. This mixes with the air that was introduced through the inlet valve. In gasoline engines with direct injection gasoline is supplied mainly in the compression stroke. In diesel engines, however, this happens at the beginning of the power stroke.
A turbocharger (also exhaust gas turbocharger) uses the energy that is lost by the exhaust gas of a reciprocating engine, profitable for driving the cylinder. It compresses the combustion air supplied to the engine, providing more torque and an increase in engine power.
In a normal reciprocating engine, the amount of air needed for combustion in the intake stroke is drawn by the piston into the cylinder. This type of engines are therefore also called ‘naturally aspirated’. For high performance engines, the movement of the piston alone is not enough to get enough air into the cylinder. Therefore turbochargers are used, which provide for a higher oxygen content in the combustion chamber of the engine.
In essence, a turbocharger consists of a centripetal turbine connected by a fixed shaft to a centrifugal compressor. The exhaust gas stream sets the turbine wheel in rotation. Its torque and speed is transmitted via the common shaft to the compressor wheel in the intake system.
How a Turbocharger works
When using a turbocharger, the thermal energy of the exhaust gases is converted into kinetic energy. The exhaust gases drive the turbine, which in turn chases fresh air through the compressor. The compressor compresses the fresh air, which is then passed through the intercooler back into the cylinder. This results in a better filling of the cylinder compared to pure naturally aspirated engines. The result is higher engine performance with lower fuel consumption and better emissions.
As long as enough exhaust gas flows, the speed is sufficient to generate an overpressure on the intake side. But this condition is reached only at higher gas flow rates from engine speeds of about 1500 to 2000 rpm, so that turbo engines operate in the lower speed range as naturally aspirated and delayed response to sudden acceleration.
The intercooler is installed between the turbocharger and the intake valve. It cools the air heated by the charge. Since cold air takes up less space, more oxygen fits into the combustion chamber. Cooling also thermally relieves components of the engine (cylinders, valves, pistons, spark plugs, etc.). Intercoolers themselves are either air or water cooled.
The Turbo Lag
In older turbochargers, a certain speed was required for the charge. In the low speed range, the amount of exhaust gas is insufficient to produce the required boost pressure for the turbocharger. Even with more modern engines, the onset of the turbocharger requires some time in stationary accelerations, since the turbine must first be sufficiently accelerated by the exhaust gas flow. As the size of the turbocharger increases, it takes longer for the compression to take place. This delay until the action of the turbocharger is called turbo lag.
Bi-turbochargers (also: twin-turbo) are two parallel turbochargers. They are powered by two cylinders of the engine, which allows them to work more efficiently.
Sequential bi-turbochargers do not charge both chargers continuously. As soon as higher engine power is demanded, the second turbocharger is activated. Typically, bi-turbochargers are installed in larger engines, where manufacturers want to keep fuel consumption low.
In addition to a regular turbocharger, the exhaust gas energy can also be utilized by the turbo-compound technology. For this purpose, an additional turbine is switched, whereby the remaining energy is transmitted in the form of kinetic energy to the crankshaft.
Turbochargers with variable turbine geometry (also VTG superchargers) have adjustable vanes on the input side of conventional turbochargers. These become steeper with increasing exhaust gas quantity, which increases the cross section.
With a VTG charger, the turbo lag can be reduced or even avoided. A large engine torque is possible in the lower and upper speed range. However, if the engine is adjusted incorrectly or the car used for sort distances only, the VTG-adjustment can be contaminated by exhaust gas residues.
VTG Turbocharger of the Porsche 911 Turbo (997). With the variable turbine geometry, the cross sections of the optimum load size are simulated by vanes that are located in the exhaust gas flow.
In addition to cars with petrol or diesel engines, turbochargers are also used in aircraft and ships. In planes, where the power of the engine decreases with increasing altitude, it can be counteracted with a turbocharger. In addition, turbochargers allow for downsizing in engine size, which saves additional weight through a smaller unit.
While in the early days the increase in performance was predominantly the reason for the engine’s charging, nowadays the main focus is on reducing emissions. For this purpose, more and more car manufacturers rely on smaller engine sizes with correspondingly optimized turbocharging.
Turbocharger: Pros / Cons
A turbocharger allows a higher maximum mean pressure and thus an increase in torque and maximum power at a given displacement. This increase either results in a more powerful engine of approximately the same size and weight as the original, uncharged engine, or allows the same power to be obtained from a smaller unit.
In addition to the many advantages, turbochargers also bring some disadvantages. The use of a turbocharger leads to higher mechanical and thermal loads as well as higher mean pressures. Therefore, many components in the engine such as e.g. Engine block and cylinder are designed to be more resistant. These measures generally increase vehicle weight.
The BMW xDrive is an all-wheel drive system, which was first introduced in the X3 and is now offered as an option for most models. The stepless and variable distribution of the drive forces through an electronic multi-plate clutch between the front and rear axles ensures greater safety and stability.
The system works in combination with the Dynamic Stability Control (DSC) and the Electronic Stability Program (ESP). The xDrive controller uses the wheel speed, acceleration, steering angle and accelerator pedal position to detect the changes in force distribution and react within a few milliseconds. The force between the axles is optimally distributed and individual wheels braked purposefully.
The xDrive in the BMW X6 (Source: manufacturer)On the newer xDrive models (expected from the new BMW M5 F90) depending on the driving mode the system can be switched to a rear-wheel drive.
☞ The all-wheel-drive system from Mercedes-Benz: 4Matic
In 1999, Mercedes had dropped the production of the inline six-cylinder engines with the last M 104. Surprisingly, in 2017 the Mercedes M 256 engine brought the long-buried in-line layout back. As a successor to the Mercedes M 276 the M 256 engine debuted mid-2017 in the new S-Class (222). In its expansion stages, the 3.0-liter unit with twin-turbo charging can deliver up to 408 hp and over 500 Newton meters of torque.
An electric boost compressor from BorgWarner and an integrated start generator ensure that the turbocharger is bypassed and the power is available from the start. As a result, the time of the turbo lag is bridged during acceleration, until the exhaust gas turbocharger kicks in.
The production of the M 256 takes place at the Mercedes-Benz factory in Stuttgart-Untertürkheim.
The 3.0-liter M TwinPower Turbo inline six-cylinder engine in the BMW M2 Coupé – in addition to its long name – stands out for its efficiency. The special features of the unit include an oil system with return pump, which ensures the correct oil supply even at extreme longitudinal and lateral accelerations.
With an output of 370 hp (272 kW) and a torque of 500 Nm with overboost, it accelerates the 1,570 kilogram BMW M2 Coupé between 1,400 and 5,560 rpm in around 4.3 seconds to 100km/h. The fully variable valve control with High Precision Injection and a TwinScroll turbocharger ensure optimum filling of the six cylinders.
The fuel consumption is combined at 8.5 liters per 100 km with a CO2 emission of 199 g/km.