Twinport With an innovative variable intake control system called "Twinport", Opel plans to reduce the fuel consumption of small gasoline engines (up to a maximum size of 1.6 liters) by as much as six percent. The smart solution employs a variable intake manifold in combination with a high rate of exhaust gas recirculation. The "Twinport" technology works in conjunction with engines with four valves per cylinder, a requirement fulfilled by Opel's complete ECOTEC range.
"Twinport" controls the supply of the fuel-air mixture to the cylinders according to the engine's actual needs. At part load, one of the two intake ports leading into the cylinder is throttled. This causes an intensive swirl effect to develop as the mixture enters the cylinder, which in turn makes the engine more economical when operating with a high proportion of recirculated exhaust gas. At full load, on the other hand, the throttling device is opened, the cylinder receives a greater charge of mixture and full power is developed. By adapting the swirl movement of the incoming charge to suit engine operating conditions, maximum fuel economy is always achieved.
"One of the advantages of the "Twinport" technology is that the proven intake-port fuel injection system and the principle of exhaust emission control by three-way catalytic converter can be retained," explains Hans H. Demant, Opel's Executive Director, Engineering. "This limits the extent of the technical modifications and in turn makes it possible to offer our customers this technical development at an affordable price. For this reason we regard variable intake control as an intelligent approach to the task of reducing fuel consumption on small gasoline engines." Extensive tests carried out by Opel Powertrain's experts have confirmed that these smaller engines, if equipped with "Twinport", can achieve at least 80 percent of the fuel savings expected from an engine using gasoline direct injection and the stratified-charge principle.
The gasoline engine's relative weakness in fuel consumption compared to diesel units is due largely to throttling losses. The easiest way of minimizing these losses is by increasing the amount of exhaust gas in the fuel-air mixture - in other words exhaust from preceding combustion cycles is recycled back into the combustion chambers and blended into the fresh mixture. However, in order to maintain rapid, stable combustion at high rates of exhaust gas recirculation, charge movement must be intensified. This is precisely what Opel's engineers have achieved with their variable intake control system: at partial load one of the two intake ports to each cylinder of the four-valve engine is partly blanked off by closing a throttle just before the mixture reaches the intake valve. As a result, the mixture enters the cylinder at an angle. This creates a swirl effect around the cylinder axis and ensures that combustion takes place reliably and completely. If the driver calls for full power from the engine, however, the second intake port is re-opened fully to make sure that the maximum mixture charge enters the cylinder.
For successful use of the shutdown principle, the intake ports and the mixture formation process before and after entering the cylinders had to be optimized. To achieve this, Opel's engineers made simultaneous use of computer-based flow simulation and video observations on actual engines. The outcome of their efforts: the modified engines reduced the car's fuel consumption by six percent when put through the standard test cycle.
In the words of Dr. Uwe-Dieter Grebe, the engineer responsible for gasoline engine development at Opel Powertrain GmbH: "Our experimental work has clearly proven that variable intake control in conjunction with high exhaust gas recirculation rates achieves approximately the same reduction in fuel consumption on small-displacement engines as the far more complex direct gasoline injection principle". Grebe's conclusions: "For the smaller engines that are used in compact and lower midsize cars in particular, "Twinport" is an intelligent and simple means of improving the engine's operating characteristics."
Wierd talk of economy then