It was big news at the time. A New York Times headline from Oct. 1, 1913, read, "Dr. Diesel Vanishes from Steamship." It was shortly before the start of World War I and Rudolf Diesel's invention had gained widespread notoriety. Quoting one of the inventor's colleagues, the story concluded, "Sidney Whitman, the oldest director of the company, is unable to offer any explanation of the disappearance. He agrees with Herr Carels that Dr. Diesel was in the best of health and spirits, saying, 'His untimely end is deeply deplored by many friends and admirers throughout the world.'"

Cyberspace speculators offer all kinds of theories on Diesel's disappearance and there is still considerable interest in the case nearly 100 years later. Perhaps one reason for such interest today is that his engine could run on many types of fuels, including vegetable oils, and he is widely touted by some in the biodiesel industry as saying shortly before his death that the "use of vegetable oils for engine fuels may seem insignificant today, but such oils may become, in the course of time, as important as the petroleum and coal tar products of the present time." This is a heavily circulated statement, and certainly the development of the biodiesel industry has led to assertions that Diesel's vision regarding the energy potential of vegetable oils is coming true.

In the United States, National Biodiesel Day takes place on March 18, the date of Rudolf Diesel's birthday. The biodiesel industry chose his birthday to honor him for his foresight in recognizing the valuable role of vegetable oil-based fuel. "Rudolf Diesel understood that fossil resources were not a bottomless barrel," says Joe Jobe, National Biodiesel Board CEO. "He foresaw that sustainable fuels like modern-day biodiesel would be a key to energy resources and continued technological advances."

Diesel's fame and his perceived commitment to agriculture have led some to speculate that he posed a threat to the rise of the black oil barons of the time, who wanted him out of the picture. That's a pretty big stretch though, says John Lienhard, former professor of mechanical engineering at the University of Houston. "Conspiracy theories always make for a dangerous area to tread," he says. "Diesel suffered from depression and his death may well have been suicide, or at least was caused by a general carelessness in regard to maintaining his life."

It's not speculation, however, to say that Diesel made many enemies during the course of his life and career. "He apparently grossly misunderstood what it meant to invent something," Lienhard says. "For one, he had a tendency to denigrate the mechanics that made his engines work and he was also involved in a lot of combat regarding claims, patents and things like that."

The possibility that the oil industry was threatened by Diesel's ideas about vegetable oils and therefore had him killed is probably a crackpot theory in the current period when the oil industry is often vilified for its high profit margins, victimization of consumers and carelessness in regard to environmental issues. The fact is that gasoline was as cheap as water during Diesel's lifetime, which is why it has taken so long for the biodiesel industry to get off the ground, even though the idea of combusting vegetable oils is almost as old as the industrial revolution itself.

Influence
It was more than 100 years ago that the company that first marketed Diesel's engine built a power plant in Kiev out of four engines that delivered 400 horsepower. To put into perspective the staple of mechanical engineering that Diesel's innovative work started, consider the fact that the same company recently built the largest power plant in the company's history in Honduras featuring 60 engines and total output of more than 245 megawatts, in excess of 500 times the capacity of the Kiev pioneer plant. "It would be easy to take for granted the significant impact Diesel's technology has had on modern life," Jobe says. "Not only did he predict the significant role alternative fuels would play, but also he developed the technology that we rely on today to move freight, commerce and, as a result, the economy."

Never able to start his own company, however, Diesel instead made a deal with a company now known as MAN SE of Munich, to market his invention. "It was very expensive to build the first diesel engine," says Ulrich Marsch of the Technical University of Munich. "So Diesel entered into negotiations with this company and he got to keep the patent, but MAN paid him to receive the first priority in marketing the engine-they made a fortune." Today MAN employs a workforce of more than 50,000 and is the world's leading manufacturer of diesel engines. "So Diesel's contribution to not only the economy of Munich but Germany-at-large has been very important," Marsch tells Biodiesel Magazine.

Rudolf Diesel's villa, built from the fortune he made with the MAN Diesel Corp., still stands in Munich today, a grand reminder of the scientific and economic influence his life and invention have had on the development of the city during the 20th century, continuing to the present day. Diesel was himself a student at TUM and there is a research fellowship named for him there today. "This allows scientists to read, write and think freely without any of the demands of industry or academia," Marsch says. "Rudolf Diesel is one of our most illustrious alumni, and his name and invention are known all over the world, and that is why we named this fellowship for him."

While Rudolf Diesel's death was premature, for the most part his legacy was intact when he vanished from the Dresden in 1913. His engine had already taken hold and captured the imaginations of industrial magnates, who for the last century have continually worked to improve his initial design. "He lost money in a patent trial and he suffered from depression all of his life, so it certainly looks like suicide," Marsch says. "Nevertheless, he remains a very inspiring figure at TUM and in Munich."

The influence of Rudolf diesel is exemplified in the legacies of several inventors who followed in his footsteps. Diesel and his invention were certainly an inspiration to Hugo Junkers, who constructed the first airplane entirely out of steel. "He knew Rudolf Diesel and the economies of the diesel engine, and realized the great potential that it had for flight," Marsch says.

Rudolf Diesel first assembled a diesel drive together with MAN engineers in its Augsburg plant, and according to the diesel engine maker it has constantly developed this technology on an ongoing basis. "With over a hundred years of experience, we are still one of the industry's prime movers," MAN states. "We are the world's leading player in the market for two-stroke engines for ocean-going vessels, and the second-largest global manufacturer of diesel gensets for power stations." In addition, the MAN group is one of the primary industrial partners of TUM and is always looking for highly-skilled mechanical engineers to improve designs and manufacturing processes. "His engines were inherently heavier and were initially used in marine and stationary applications," Lienhard tells Biodiesel Magazine. "Only later were they used in transportation vehicles…it wasn't until several years after his death that the first truck had a diesel engine."

While it's nostalgic to look back in history and note that vegetable oils were identified as being well-suited for diesel engines early on-some might say even prescient of some of today's policy discussions-there is a gap of almost 100 years where a lot more effort went into proving, refining and innovating the engine technology rather than with the fuel it burned. Incremental refinements in diesel engines and meeting emissions milestones have really characterized 20th Century diesel history. Only recently-a century later-has the interest in biofuels become more significant.

For better or worse though, the world made choices along the way-becoming more of a gasoline-driven economy than one run predominantly on diesel, and
displaying less overall interest in renewable fuels, bowing to the availability of
cheap oil.

"In my opinion, it would be hard to draw a straight line back to Rudolf Diesel in the early days making an engine run on vegetable oil and say that is directly responsible for the interest in biofuels today," says Allen Schaeffer, executive director of the Diesel Technology Forum. "Arguably, the opposite is truer: had the fascination and interest with biofuels from Rudolf Diesel continued on the same trajectory as engine development and expanded use in industrial sectors, biodiesel today would be well incorporated into our diesel fuel pool as a mainstream component, probably surpassing ethanol's standing."

Nicholas Zeman is an associate editor for Biodiesel Magazine. Reach him at (701) 738-4972 or nicholas.zeman@bbiinternational.com.