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.