Gasoline engines are about 15%-25% efficiency. New cars are at the 25% end. Diesel engines are 30%-49% efficient. Diesel semi trucks are about 35%. Large multimegawatt diesel power plant engines are up to 49%. (See Wartsila engines).

In the patent database ESPACENET, you can locate and download for free a patent of around 1929, one of the inventors had the surname 'Thyssen', about an internal combustion turbine engine that was reported obtaining in the actual testing a thermodynamic efficiency of around 31%, very good even for today. A 30-49% efficiency in transforming the thermal energy in the fuel after burning it, changing the chemical energy of fuel into mechanical power sounds to me in the top figure as too high to be true, losses in engines are from friction and other mechanical loads, heat lost to the cooling system, and some other things I don't remember now, but as I'm not an engineer nor an expert in thermodynamics, probably my assertion contains some misunderstandings of the subject. A good reference about engines, at least for hobbyists like me, are the frequently updated series of manuals by Bosch on the technology of automobile, and also SAE.org offers a good book on the history of engines, by the Japanese T Suzuki, entitled 'The romance of engines', they were good to me, but I don't know if it will be enough for your needs.

http://www.wartsila.com/en/power-plants/technology/combustion-engines/gas-engines state the maximum efficiencies actually being achieved that are commercially available today. More generic efficiencies are at https://en.wikipedia.org/wiki/Engine_efficiency.

A nice and promising design and concept. In line not too much apart from this, you may look at the 5 Stroke ILMOR 5-engine, that has a precedent cited in the T Suzuki book, in an idea of Otto himself in the XIXth century, spanish patents 0156621, 0230551, 0249247 and 0433850, by F Jimeno-Cataneo, J Ortuño-Garcia (Ortuno) 2 patents, and C Ubierna-Laciana recorded also innovative ideas in reciprocating internal combustion engines, hope you enjoy this. Salut +

To Miles Palmer: Sorry, the efficiency figures you spoke about are real, I was stuck in first two thirds of XXth century. I remember having send Wärtsilä a question about the appropiateness of using the production tools of the Ingersoll-Rand 42 liter natural gas powered Wankel Rotary Combustion Engines for re-starting producing these RCEs for use in ships intended for Gas transport. As stated elsewhere, I really like Single-Sleeve-Valve distribution (Burt-McCollum), that was used with success in very large engines, such as the Brotherhood engine that can be watched in YouTube

Try the attached link for a most comprehensive study and evaluation of the complete energy efficiency chain in the automotive sector. This so called "well-to-wheel" study was performed as a collaboration by the Joint Research Center of the European Union (JRC), CONCAWE (an oil industry association) and EUCAR (the joint R&D organization of the European car manufacturers).

http://iet.jrc.ec.europa.eu/about-jec/downloads

To M Palmer and U Eberle: this is the engine design I like more, besides Wankel Rotary Combustion Engines

http://youtu.be/4svUFasZnz8

GM is reported having conducted research on Single Sleeve-Valve engines for cars, and having discarded this arrangement. A review on the Sleeve Valve subject at an student's level exists in Wikipedia

An early XX century patent, available for free download in ESPACENET, one of the inventors/applicants has the surname 'Thyssen', is about an internal combustion turbine with an efficiency of 31%