The Detroit Diesel Series 51 was a two stroke diesel engine. Two versions were produced, an inline two cylinder and an inline four cylinder model. It was a simplified version of the 53 series that did not have exhaust valves. This was accomplished by using scavenger ports for both intake and exhaust, similar to a two cycle gasoline engine. Since the Diesel fuel is injected just after top dead center virtually no unburnt fuel is expelled in the exhaust unlike a two cycle gasoline engine. The elimination of exhaust valves reduced the complexity and weight of the engine. This allowed the engine to be more portable and easier to service. Its uses include: Marine propulsion, generators, pumps and other industrial uses. It was never used for automotive purposes.