Environmental Engineering Reference
In-Depth Information
8.10 (a) Karl Benz's pioneering vehicle (courtesy of Daimler-
Chrysler Classic Konzernarchiv, Stuttgart). (b) Decline
of weight/power ratios of automotive and aero engines
(Smil 2005a).
has been surprisingly conservative. Major historical shifts
have included a steady rise in compression rates, an in-
crease in average power, and a decline in weight/power
ratios. In the United States typical compression ratios
rose from about 4 in the early 1920s to about 10 by the
1960s, then declined slightly, averaging 8-9 by the mid-
1980s. The first mass-produced car, Ransom Olds'
Curved Dash, had a single-cylinder 5.2 kW engine;
Ford's model T (16 million produced between 1908-
1927) had a four-cylinder 15 kW engine; and most
passenger cars built at the beginning of the twenty-first
century were powered by engines rated between 85 kW
(Honda Civic) and about 450 kW (most powerful
Mercedes).
Otto's engine needed nearly 270 g/W in 1880,
Daimler and Maybach's radical redesign brought the
ratio down to 40 g/W by 1890, the best ratios
approached 5 g/W before the end of the century, and
since then the ratio has declined to as low as 3 g/W for
trucks and about 1 g/W for passenger cars. The decline
of weight/power ratios was much faster for aircraft
engines (Gunston 1986). A four-cylinder engine power-
ing the Wright brothers' first flight on December 17,
1903, rated 9.1 g/W; the U.S. V-12 Liberty engine
