Twin-scroll turbocharger designs have two exhaust gas inlets divided by split walls inside the turbine housing, with both gas passages controlled by a waste-gate. A twin-scroll turbo recovers even more energy from the exhaust than a single-scroll turbocharger thanks to a divided manifold. The twin-scroll design separates the cylinders whose exhaust gas pulses interfere with each other resulting in improved pressure distribution in the exhaust ports and a more efficient delivery of exhaust gas energy to the turbochargers turbine.
For example, at the start of the intake stroke of cylinder one, and when both the intake and exhaust valves of cylinder one are open (valve overlap period), cylinder three already starts its exhaust stroke with the exhaust valve open. If the exhaust passages of cylinder one and three were connected, the exhaust gas pulse from cylinder three would increase the back pressure of cylinder one. This would reduce the induction of the fresh air and increase the amount of hot residual gases inside the cylinder. However, with the twin-scroll turbocharger setup, this interference is minimized.
The result of this superior scavenging effect from a twin-scroll design leads to better pressure distribution in the exhaust ports and a more efficient delivery of exhaust gas energy to the turbocharger’s turbine. This in turn allows greater valve overlap, resulting in an improved quality and quantity of the air charge entering each cylinder. In fact, with more valve overlap, the scavenging effect of the exhaust flow can literally draw more air in on the intake side. At the same time, drawing out the last of the low-pressure exhaust gases help pack each cylinder with a denser and purer air charge. Maximum boost from the turbocharger is 17.4 psi.
The twin-scroll turbocharger design has several other advantages over traditional, single-scroll turbocharging systems, including:
Improved combustion efficiency
Low engine-speed efficiency
Kinetic exhaust gas energy is not wasted or trapped
Cooler cylinder temperatures
Lower exhaust temperatures
Leaner air/fuel ratio
Better pressure distribution in the exhaust ports and more efficient delivery of exhaust gas energy to the turbocharger’s turbine
Essentially, Sonatas twin-scroll turbo directs even more air into the engine while a compressor increases the pressure entering the cylinder. This allows the air entering the cylinder to be even more densely packed for higher compression and better performance, contributing to a more-efficient burn and fuel efficiency.
Two key features of Hyundais twin-scroll turbocharger setup are:
1. The stainless steel exhaust manifold and the twin-scroll turbine housing are cast in a patent pending one-piece design
2. The waste-gate for the turbocharger uses a motor-driven electrical controller instead of being mechanically controlled
Thanks to the integrated stainless-steel turbine housing with the exhaust manifold, not only is the weight and cost of the casting dramatically reduced, the durability of the turbine housing is also improved.
By adapting the motor-driven electrical waste-gate, the boost pressure is precisely controlled. The back pressure is reduced when turbo boost is not necessary by opening the waste-gate, which improves fuel efficiency. In addition, during cold starts, the waste-gate remains open which results in faster catalyst light-off for reduced exhaust emissions.
A GDI fuel delivery system contributes to improved fuel efficiency and lower emissions. This shorter, more direct path of fuel delivery allows for greater control of the fuel mixture at the optimum moment, thus improving efficiency. The fuel is injected by a camshaft-driven, high pressure pump that operates at pressures up to 2175 psi. Direct injection also utilizes a higher-than-normal 9.5:1 compression ratio while achieving a remarkable 137 horsepower-per-liter. The piston heads are dished to increase combustion efficiency in the cylinder.