Nikhil
Honorary ///Member
Variable geometry VNT turbo vs. fixed geometry turbo
Many turbodiesel engines feature variable vane, variable geometry, or variable nozzle technology that is only now being used in gasoline engines. A gasoline engine's sustained exhaust temperatures are higher than in a diesel, which resulted in damage and short lifespans for early gasoline variable turbos during the 1980s. Gasoline engines also require the turbo to be more efficient over a larger range of rpm as compared to a diesel engine. Today, advances in turbo design and metallurgy have made these turbos more reliable on both gasoline and diesel cars, although only one gasoline car, the newest Porsche 911 turbo, currently uses it.
Variable vane, variable geometry, or variable nozzle technology change the angle which the exhaust pushes against the exhaust turbine. This greatly reduces lag while keeping top end power. It combines the fast spool of a small turbo with the flow capacity of a larger turbo. Different types of variable turbos have different ways of accomplishing this with vanes or nozzles. By optimizing the speed and angle of the exhaust moving through the exhaust housing and hitting the turbine, it maximizes the efficiency of the turbo. By keeping the turbo speed higher over a greater range, it produces more low end power with sustained top end with about equal amounts of airflow compared to a traditional turbo. This VW turbodiesel engines mk4 (4th generation) and newer, starting in 1998 with the New Beetle all use a variable geometry turbocharger.
Below are 2 youtube movies showing how it works. There's a vacuum can which moves a lever in the exhaust side of the turbo hosing. Vacuum is being applied to the can, not pressure. To see disassembly of a VNT turbo on a ALH engine TDI, see 1000q: VNT vane removal and cleaning. Some newer TDI use an electric motor to move the rod instead of a vacuum can.[video=youtube]
also check myturbodiesel.com
hope its not a repost :=):
Many turbodiesel engines feature variable vane, variable geometry, or variable nozzle technology that is only now being used in gasoline engines. A gasoline engine's sustained exhaust temperatures are higher than in a diesel, which resulted in damage and short lifespans for early gasoline variable turbos during the 1980s. Gasoline engines also require the turbo to be more efficient over a larger range of rpm as compared to a diesel engine. Today, advances in turbo design and metallurgy have made these turbos more reliable on both gasoline and diesel cars, although only one gasoline car, the newest Porsche 911 turbo, currently uses it.
Variable vane, variable geometry, or variable nozzle technology change the angle which the exhaust pushes against the exhaust turbine. This greatly reduces lag while keeping top end power. It combines the fast spool of a small turbo with the flow capacity of a larger turbo. Different types of variable turbos have different ways of accomplishing this with vanes or nozzles. By optimizing the speed and angle of the exhaust moving through the exhaust housing and hitting the turbine, it maximizes the efficiency of the turbo. By keeping the turbo speed higher over a greater range, it produces more low end power with sustained top end with about equal amounts of airflow compared to a traditional turbo. This VW turbodiesel engines mk4 (4th generation) and newer, starting in 1998 with the New Beetle all use a variable geometry turbocharger.
Below are 2 youtube movies showing how it works. There's a vacuum can which moves a lever in the exhaust side of the turbo hosing. Vacuum is being applied to the can, not pressure. To see disassembly of a VNT turbo on a ALH engine TDI, see 1000q: VNT vane removal and cleaning. Some newer TDI use an electric motor to move the rod instead of a vacuum can.[video=youtube]
also check myturbodiesel.com
hope its not a repost :=):
