Engine Technologies (2)

As a continuation to the previous post....

Variable Geometry Turbocharger:
     Variable Geometry technology is the next generation in turbocharger technology where the turbo uses variable vanes to control exhaust flow against the turbine blades. The problem with turbocharger that we’ve all come to know is that big turbos do not work well at slow engine speeds, while small turbos are fast to spool but run out of steam pretty quick. So how do VTG turbos solve this problem?

      A turbocharger equipped with Variable Turbine Geometry has little movable vanes which can direct exhaust flow onto the turbine blades. The vane angles are adjusted via an actuator. The angle of the vanes vary throughout the engine RPM range to optimize turbine behaviour.

     In the above image, the direction of exhaust flow when the variable vanes are in an almost closed angle. The narrow passage of which the exhaust gas has to flow through accelerates the exhaust gas towards the turbine blades, making them spin faster. The angle of the vanes also directs the gas to hit the blades at the proper angle.



     Image shows the exhaust gas flow when the variable turbine vanes are fully open. The high exhaust flow at high engine speeds are fully directed onto the turbine blades by the variable vanes.

Vanes of Turbocharger at closed position

Vanes of Turbocharger at fully opened position



Variable Valve timing and Lift Electronic Control:

     VTEC (Variable Valve Timing and Lift Electronic Control) is a valvetrain system developed to improve the volumetric efficiency of a four-stroke internal combustion engine. This system uses two camshaft profiles and electronically selects between the profiles. Due to the behavior of the working fluid (air and fuel mixture) before and after combustion, which have physical limitations on their flow, as well as their interaction with the ignition spark, the optimal valve timing, lift and duration settings under low RPM engine operations are very different from those under high rpm.

     Optimal low RPM valve timing, lift and duration settings would result in insufficient filling of the cylinder with fuel and air at high RPM, thus greatly limiting engine power output. Optimal high RPM valve timing,lift and duration settings would result in very rough low RPM operation and difficult idling.The ideal engine would have fully variable valve timing, lift and duration, in which the valves would always open at exactly the right point, lift high enough and stay open just the right amount of time for the engine speed in use.

     Some later variations of the system were designed solely to provide improvements in fuel efficiency, or increased power output as well as improved fuel efficiency.

Engine Technologies (1)

Hi All,


As this is my first post I would like to go with Engines of automobiles to give myself thrust as well.

    I also want to make clear that I am posting this only for brief information and I am not going to make in depth analysis as a Scientist.

   Coming to the topic, many of us have seen something written on the back/side of cars entering markets like CDI, CRDI...This is an attempt to sort out confusion and to give a brief idea about them.


Engine Technologies that have been developed to reduce emission, improve fuel combustion, improve fuel efficiency, improve power output are 

• Homogenous Charge Compression Ignition (HCCI)
• Common Rail Direct Injection (CRDI)
• Turbocharged Direct Injection (TDI)
• Twin Charger/Turbocharger Supercharger Injection (TSI)
• Variable Geometry Turbocharger
• Variable valve timing,lift systems and active fuel management
• Stratified Charge Injection

Homogenous Charge Compression Ignition:

     The Homogeneous Charge Compression Ignition (HCCI) is a combustion system where a homogeneous air/fuel mixture is ignited by compression.It has the potential to improve efficiency without requiring complex lean exhaust after treatment, helping to deliver a fuel savings of 15%.

     An HCCI engine is a mix of both conventional sparkignition and diesel compression ignition technology. The blending of these two designs offers diesel-like high efficiency without the, difficult and expensive to deal with, NOx and particulate matter emissions.

Advantages of HCCI:

1. Lean combustion returns 15 percent increase in fuel efficiency over a conventional spark ignition engine.
2. Cleaner combustion and lower emissions (especially NOx) than a conventional spark ignition engine.
3. Compatible with gasoline as well as ethanol fuel.
4. Fuel is burned quicker and at lower temperatures, reducing heat energy loss compared to a conventional spark engine.
5. Throttleless induction system eliminates frictional pumping losses incurred in traditional (throttle body) spark engines.

Disadvantages of HCCI:

1. High cylinder pressures require stronger (and more expensive) engine construction.
2. More limited power range than a conventional spark engine.
3. The many phases of combustion characteristics are difficult (and more expensive) to control.

CRDI:
     Common rail direct fuel injection is a modern variant of direct fuel injection system for petrol and diesel engines. On diesel engines, it features a high-pressure (over 1,000 bar) fuel rail feeding individual solenoid valves, as opposed to low-pressure fuel pump feeding unit injectors.Third generation common rail diesels now feature piezoelectric injectors for increased precision, with fuel pressures up to 1,800 bar.
     In gasoline engines, it is utilised in gasoline direct injection engine technology. Fuel in the common tube or “rail” is under a set amount of pressure which causes the fuel to be “atomized” or broken down to its smallest particles.With proper direct injection, fuel use is highly efficient, with much less waste fuel escaping the system unused.
      The electronic technology has also allowed CRDI engines to better control the amount of fuel used, the pressure within the system and the timing of both the injection of fuel and the electronic charge applied to make the fuel burn. Injectors have controls on the injector heads that allow slight variances in the amount of fuel put into the cylinders.

Common rail fuel injector

CRDI for diesel vehicles has improved performance by as much as 25 percent.

Sketch showing Common rail system in an engine

Advantages:

1. Solenoid or piezoelectric valves make possible fine electronic control over the fuel injection time and quantity.
2. The higher pressure available provides better fuel atomisation.
3. Engine's electronic control unit injects a small amount of diesel just before the main injection,thus reducing its explosiveness and vibration, as well as optimising injection timing and quantity for variations in fuel quality, cold starting and so on.
4. Some advanced common rail fuel systems perform as many as five injections per stroke.
5. Common rail engines require no heating up time and produce lower engine noise and emissions than older systems.

Turbocharged Direct Injection(TDI):

    TDI or Turbocharged Direct Injection is a design of turbodiesel engines,which feature turbocharging and cylinderdirect fuel injection. The TDI engine uses direct injection, where a fuel injector sprays atomised fuel directly into the main combustion chamber of each cylinder. The engine also uses forced induction by way of a turbocharger to increase the amount of air entering the engine cylinders. These, in combination, allow for greater engine efficiency, and therefore greater power outputs (from a more complete combustion process), while also decreasing emissions and providing more torque.

Twin Charger/Turbocharger Supercharger Injection (TSI)

     It is a combination of an exhaust-driven turbocharger and an engine-driven supercharger, each mitigating the weaknesses of the other. A belt-driven supercharger offers exceptional response and low-RPM performance as it has no lag time between the application of throttle and pressurization of the manifold.
     Combined with a large turbo which would offer unacceptable lag and poor response in the low-RPM range, the proper combination of the two can offer a zero-lag powerband with high torque at lower engine speeds and increased power at the higher end.

Sketch showing Twin chargers installed over an Engine

The next technologies I'll discuss in next post.