Packard DR-980 9 cylinder radial Diesel engine. Only about 100 were ever built, but they were eventually certified airworthy.....in 1930! This engine produced 225 horsepower continuously at 1,950 RPM. The usual Diesel challenges of vibration and strong exhaust smell caused many pilots to dislike them, but the design still proved to be reliable and very economical to operate.
A DR-980 set an 84 1/2 hour endurance record for flight on one tank of fuel in 1931. This record would go on to stand for 55 years..