Inverted Atkinson Cycle in Ford EcoBoost Engines

By Raul J.

Atkinson Cycle usully works by leaving opened the admission valve at the beginning of the compression stroke, allowing for a higher expansion ratio in the combustion that increses efficiency, but also generating a blowback of fresh air into the intake ports that reduces much of the efficiency gained.
In the proposed Inverted Atkinson Cycle, the exhaust port opens again at the end of the admission stroke and keeps opened at the beginning of the compression stroke, so part of the intake air bypass the combustion cycle and is sent straing to the exhaust, allowing again for a higher expansion ratio that increases efficiency but without blowback into the intake port. There is a second benefit as this bypass air collects heat from the cylinder before leaving by direct contact with the walls and valves, cooling the combustion chamber.
The operation of this cycle requires direct injection of fuel, that is standard in Ford Ecoboost Engines, as part of the intake air bypass the combustion cycle. As the engine chamber is cooler at the start of each combustion cycle, the maximum temperature is also lower, avoiding the requirement of a NOx Catalyist and allowing the operation in lean combustion conditions, further increasing efficiency.
In turbo or supercharger engines, as Ford Ecoboost, the effect of the turbine/supercharger is cooling the engine by increasing the bypass ratio of air that goes straight to the exhaust, instead of increasing the pressure in the intake air. As much of the waste heat would be removed by operation of the turbine, the cooling system can be downsized thus simplifying the engine and further increasing efficiency. Also, as the pressure is not incresed, most of the disadvantages of turbo engines dissapear, as there is not necessity of intercooler in the intake port or reducing the compression ratio in the engine, or reinforcing the engine.
In summary:
The cycle operates by opening againg the exhaust valve at the end of the admission stroke and leaving it opened at the beginning of the compression stroke.
This operation allows for a higher expansion ratio that increases efficiency, but not generates a blowback of fresh air into the intake port, but a bypass into the exhaust port.
The bypass generates and extra cooling of the combustion chamber, reducing its temperature and avoiding the generation of NOx
In turbo engines, the effect of the cycle is increasing the bypass ratio of fresh air and therefore the cooling of the engine, reducing the requirements of the cooling system.
Compared with standard EcoBoost engines, the proposed system would be:
More efficient, as compression and expansion ratios would be higher.
More simple, as there would be no NOx Catalyst and no intercooler, and the cooling system would be downsized. Also, thermal and pressure loads of the engine would be lower.
victor goodman 03/18/2014
Bypassing the cylinder and cooling before the compression stroke is a very bad idea. The engine is a heat engine. The hotter it and the burning fuel mixture gets, the greater is the efficiency. Example: off-brand thermostats often open up at lower temps than the manufacturer specifies. When the temp is low, the fuel efficiency drops. happened to me with a ford product. Also, so what if the intake closes late and blows back air into the intake manifold? The pumping losses are lower still.
The Ecoboost 2.0L has lower compression than the NA 2.0 found in the focus... and gets worse mpg (though it is more powerful)
Steve Round 04/16/2013
Whatever happened to the sleeve valve engine - what with the reaisation of much improved combustion chamber design and vastly improved metalurgical knowledge and practise this could revolutionise engine design. People forget that the short stroke 24 cylinder horizontal H profile Napier Sabre aircraft engine produced over 5000 hp in 1945 and weighed hardly any more than the merlin (1600hp) - and could run reliably on very low octane fuel because no inlet or exhaust valves were involved. Napier were once THE leading light in all kinds of engine development from before 1918 till 1945! Rolls Royce copied theyr Sabre aircraft enging because it was the most promising piston engine developed by any of the contestants during the whole of the Second World War. No other aircraft engine manufacturer produced half the rated power of the Napier Sabre this engine stood head and shoulders above every other piston propelled aircraft engine developed by anyone anywhere during this time!
Raul J 12/28/2012
Yes, the mission of turbo would not be to provide extra oxygen and the car would work always as an atmospheric, as the extra air provided for the turbo is lost before compression, but after it has cooled the combustion chamber and provided usabe work during the admission stroke.
Improvements in efficiency are supposed to come from a higher compression ration, reduced thermal stress to the engine, and the compounding provided during the admission stroke.
I agree with you in that the idea is still a theoretical rainbow after three years. But turbos have been around for one century and still don´t work properly in cars, so three years are not so much time.
mike 09/07/2012
Opened valves during compression, either intake or exhaust, seem to guarantee less available oxygen during detonation. Efficiency increases thus seem even possible only marginally. I'd guess the cost-saving inherent in eliminating the catalyst is the end of the theoretical rainbow here, not overall efficiency increases.