The efficiency of diesel engines can be increased if the energy in the exhaust gases were better utilized. The invention (USPTO 8,210,136) shown here allows the hot combustion gases to expand a second time within the engine. The power from that secondary expansion is used by the other cylinder’s supercharger. This invention is a two-stroke diesel engine with opposed cylinders. The engine is modular in that additional pairs of cylinders can be ganged together to form a larger flat engine with a central crankshaft.

Here is how it works. The first figure shows a pair of cylinders. Near the end of the power stroke, combustion gases are released to the secondary expansion chamber. A single large valve at the bottom of the combustion chamber allows this. The continued expansion pushes a piston that is directly connected to the opposite cylinder’s supercharger. That supercharger is compressing. At the end of the stroke, the gases in the secondary expansion chamber are cooler and at lower pressure. The gases are cooler because some of its heat has been converted into extra power. The lower pressure reduces the exhaust noise.

Thermodynamic curves shown in the second figure compare this new engine design to a traditional diesel. The Pressure-Volume (P-V) curves are at the top. The area enclosed by the P-V curve is proportional to the engine’s net power. The area of the YankeeDiesel is larger because the power stroke is extended by the additional expansion. The Temperature-Entropy (T-S) diagram is another efficiency indicator. The YankeeDiesel’s lower exhaust temperature means that less heat is exhausted and more mechanical power is produced. The thermodynamic state analysis was done using algorithms in www.thermofluids.net

A traditional crankshaft with connecting rods would prevent opposed cylinders from helping each other. This new design required a planetary crankshaft which eliminated the connecting rods and a separate camshaft. A partially assembled model of a four cylinder engine is shown in the third figure. The supercharger and secondary expansion chamber are coupled together with the planetary crankshaft as shown with the insert in that figure. The design has progressed through several iterations; details can be seen at www.yankeediesel.com