New York Central
What a sweet art deco inspired aerodynamics package! That's one awesome looking locomotive. 
That is a real locomotive, a 1938 Mercury Streamliner 20th Century Limited designed by Henty Dreyfuss for the New York Central Railroad and built by Baldwin Locomotive Works of Philadelphia, Pennsylvania. Yup, it was a steam powered, not Diesel, locomotive.
You are quite right, sir! But, it still fits with the dieselpunk genre because of its design, not its engine power. The 30s and 40s were still the age of steam engines, but one would never consider them steampunk. In any case, it’s an awesome 4-6-2
Frankly, I consider it as a real rolling piece of art. It is from 83 years ago but it still looks futuristic. It is from an era when many industrial machines were so beautiful like a 1936 Stutz Bearcat or a 1935 Duesenberg, which was so much better than any Mercedes, Cadillac or any luxury car of that era and made in Fort Wayne, Indiana.
If you wonder where that expression " It's a Doosy " came from, Duesenbergs were called Doosys and the expression means it's by far the best.