Double scroll technology
When optimizing engine performance with the objective of minimizing fuel consumption and engine emissions, ideally this should be achieved without a penalty in engine responsiveness. From this perspective, a swift and highly dynamic turbocharger performance over a large engine operating range is preferred for downsized engines. Among others, such a turbocharger performance can be achieved through application of multiple-entry turbine concepts. When applying a multi-entry turbine, one can maximize the potential of the pulse energy present within engine exhaust gas. By doing so, not only stationary but also transient turbine performance is improved. This will result in a more reactive turbocharger with a minimum response time or so-called ‘turbo lag’.
Where Twin Scroll and bi-turbochargers are commonly used on engines with 4 or more cylinders, the next level of pulse Turbines is a segmented turbine, also known as a double scroll turbine. Such a turbine has radially dived scrolls instead of circumferentially dived scrolls often designated as ‘twin scroll’ technology.
The big advantage of double scroll technology is in the separation level between both volutes. This improves the scavenging behavior significantly. Also, the pulse energy of each cylinder is transferred in an efficient way to the Turbine inducer.
The drawback of double scroll technology is that the high separation level between the volutes increases the turbine inlet pressure at rated power. To deduct this effect, Mitsubishi turbocharger division has also developed several concepts of scroll connection devices. The scroll connection device strives to let the double scroll turbine work like a “Monoscroll”. Scroll connection devices can both work separate or integrated in the waste gate function.