Orbital’s DI Technology Saves More Fuel
Australian-based Orbital’s OCP (Orbital Combustion Process) direct-injection (DI) technology had achieved a new level of capability in the automotive sector. During extensive testing of the system, Orbital achieved a vehicle fuel economy improvement in excess of 20% over the European test cycle while still meeting the tough EURO 4 emission control requirements.
The results were achieved without modification to the baseline vehicle and demonstrated a very high reduction (up to 90%) in engine-out oxides of nitrogen (NOx). The very low NOx emissions enabled the use of a relatively low cost catalyst aged to simulate conditions at high mileage. The catalyst was developed in conjunction with Johnson Matthey, one of the world’s leading producers of automotive catalysts.
“The 20% improvement takes OCP into a league of its own, in terms of real world fuel economy improvements from a single tchnology change. When you look at the combustion system alone, the alternative stratified charge direct injection systems do not show more than a 5-10% improvement under driving conditions in Europe,” said Kim Schlunke, Orbital’s CEO. “Indeed, if Orbital’s technology were applied in combination with typical additional vehicle refinements, such as electric power steering and weight reduction, we would expect a fuel economy improvement in excess of 25%.”
In the US, fuel quality limitations have so far prevented significant penetration of petrol DI technology. However, the inherently low NOx emissions of Orbital’s combustion system will enable the technology to work in the US emissions environment. This means that a single technology change would have a significant impact on the Corporate Average Fuel Economy (CAFE) performance of major US automobile manufacturers.
The average fuel economy of cars and light trucks sold in the US is at it’s worst since 1981 which has placed US automakers under intense pressure to improve their CAFE performance. Orbital is hoping its breakthrough will draw their serious attention.
The fuel economy capability is particularly important to Orbital’s automotive customers as they look to the future requirements for greenhouse gas reduction in the global market. In Europe, for example, the major automakers have committed to a vehicle fleet average CO2 target of 140 g/km by 2008, which will require on average a 35% reduction from current fleet fuel consumption figures. Orbital’s latest achievement will obviously be able to contribute significantly towards this goal.
The fuel economy results were achieved in a standard 4-door sedan powered by a 2.0-litre, 16-valve 4-stroke engine converted to run the latest version of the OCP DI fuel system. The test engine incorporated major developments of the air and fuel supply systems as well as further refinement of the engine calibration and control system.
“The last few years have been a new learning experience for automotive companies as they have found that laboratory predictions for the performance of competing DI fuel systems have not always transferred into their on-road vehicles”, added Mr Schlunke.
“Orbital has continued to develop a robust direct injection combustion system which can deliver major fuel economy improvements in the real world. A key feature of Orbital’s unique system is the use of low-pressure air as the propellant which produces very small fuel droplets that contribute significantly to the robustness of the system. This is one of the key factors that enables the laboratory test data to be transferred into a real world vehicle application The OCP robustness has been discussed in detail in a recent publication by Orbital at the Japan Society of Auto Engineers Conference,” he said.
Orbital has been developing OCP technology for 4-stroke automotive applications for over five years, with previous announcements in 1999 and 2000 detailing the technical capability of the system and the commitment of customers such as Saab for future production programs. Orbital is today a leading international developer of engine technologies using direct in-cylinder fuel injection and lean-burn systems for enhanced fuel economy and lower emissions.
The Orbital Combustion Process
The breakthrough in engine design achieved by Orbital is a stratified combustion process, which involves an air-assisted injection of fuel directly into the combustion chamber and uses electronic control of the fuel delivery, injection timing, ignition and other variables.
The OCP and control is suitable for both 2-stroke and 4-stroke engines and has been applied successfully across a range of cylinder displacements from 50 cc to greater than 500 cc, including high speed engine operation.
In a conventional engine, the fresh fuel/air mixture is prepared upstream of the cylinder (whether by carburettor or conventional EFI) and enters the cylinder during the intake stroke, with the intent of forming a homogenous mixture of air and fuel within the cylinder.
The application of OCP technology enables systems allow a highly stratified combustion process to occur, containing the combustible fuel cloud to a small area within the cylinder, with the remainder of the air in the cylinder being not fuelled.
This process at light loads allows engines with OCP to run very lean (in some cases, total engine operation is carried out without the use of an air intake throttle). Under high load conditions, the OCP system runs similar to a homogeneously-charged engine, with good mixing of the fuel/air mixtures within the cylinder.
In the case of a 2-stroke engine, direct fuel injection is possible after the exhaust port closes at light loads, minimising the short-circuiting of fresh fuel/air mixture out of the exhaust port as occurs in conventional 2-stroke engines. In the case of a 4-stroke engine, direct fuel injection allows lean engine operation, significantly reducing the engine pumping work.
The combustion process, due to control of the air to fuel ratio gradient within the spray plume, allows clean and controlled combustion, resulting in further improvements in fuel economy and emission control.
Apart from the basic combustion process and the associated fuel and control system, Orbital has developed related technologies including catalyst systems, control systems, control hardware and control software for vehicle applications of engines using OCP technology.
