Double expansion – a four stroke engine with eight cylinders
The LRT engine block differs a lot compared to traditional engine designs with four conventional combustion cylinders and four auxiliary cylinders. The auxiliary cylinders provides energy recovering of exhaust pressure and temperature. Converted to mechanical energy directly to the crankshaft. By integrating these auxiliary cylinders in the engine`s block, the engine design offers a short transport road for the exhaust gases . This compact design minimize pressure- and temperature losses to gain high efficiency.
After the combustion cylinders has finished its expansion , the associated discharge valve is opened and the exhaust will be transferred to the two upper and lower expansion cylinders whose pistons are in top position. The residual exhaust pressure then forces the two expansion pistons downwards. As they reach the bottom position, the final exhaust valves open and the exhaust from both auxiliary cylinders as well as from the actual main cylinder is released to the open air during the next 180° rotation of the camshaft.
The same cycle is repeated over the next 360°, but this time with the other main cylinder as the pressure delivering cylinder. That means the expander is working in two-stroke mode. The LRT Engine operates four ordinary combustion cylinders and four auxiliary cylinders, which act as gas expanders. LRT enables an engine design that offers double expansion where a significant part of the residual power in the exhaust is also fed to the engine shaft.
Theoretical studies done by the University in Agder, estimates the improvement in fuel efficiency to be 15 %. This principle works both in spark ignited engines and in compression ignited engines.