Some of those technologies have led environmentalists to declare the 100-plus-year-old internal combustion engine "dead."  But, thanks to a digitally controlled latching valve invented by aerospace engineer Eddie Sturman in the 1960s, the internal combustion engine has been rehabilitated and, with that, a fourth propulsion alternative has been created.

Eddie Sturman's journey into automotive propulsion technology began in the 1960s while working in NASA's Apollo moon landing program.  At that time, Sturman invented a digital valve that could be controlled and latched in position through pulse modulation.  Because the latching process invented by Sturman uses only a very minimal amount of electric current to hold the valve open, the valve proved invaluable in aerospace applications where energy conservation is mandatory.

When the energy crisis developed in the early 1970s, Sturman, who was working for Bell Aerospace at the time, proposed using his patented digital valve technology to increase fuel efficiency in automotive applications.  Because Bell Aerospace exhibited no interest in the automotive market, Sturman quit Bell and formed his own company.

While developing automotive applications for his digital valve, Sturman developed a battery-powered, stand-alone wireless irrigation system that used the digital valve to efficiently irrigate the desert farmlands of Israel.

After selling his original company, Sturman moved on in 1980 to head research and development at the Parker-Hannifin company, which did consulting work in hydraulics and valves for heavy-equipment powertrain manufacturers such as Cummins, Caterpillar, Perkins, and Eaton.

In 1989, however, Carol and Eddie Sturman founded Sturman Industries in California and plunged into the consulting, research, and development phase of powertrain engineering.  After two years of searching for a "facility suitable for innovation," the couple settled on relocating Sturman Industries to Colorado in 1995.

As for rehabilitating the internal combustion engine (ICE), Sturman said, "The four-cycle or Otto cycle principle for operating internal combustion engines has been in existence for over 100 years." 

In the familiar Otto cycle, the ICE spends its first crankshaft revolution on the intake stroke to draw an air charge into the cylinder and then to compress it on the upward stroke.  In a gasoline application, the fuel is mixed with the air and ignited by an electric spark. 

 
In a diesel application, the fuel is injected directly into the engine's combustion chamber and is ignited by heat from compression. 

The second crankshaft revolution is spent burning a fuel charge on the power stroke and exhausting it on the exhaust stroke.  All of these ICE events are controlled by a mechanical camshaft operating against a set of springs used to hold the valves in a closed position.

"Unfortunately, the mechanically actuated ICE engine can only be optimized to operate at a single speed," Sturman said.  By using a computer-controlled digital latching valve to eliminate the mechanical camshaft, Sturman has, in effect, created an internal combustion engine that can be optimized for any engine speed, any fuel, and any operating condition. 

 
"The digitally controlled engine can efficiently burn petrol diesel, biodiesel, gasoline, or ethanol fuels with no exhaust emissions.  The digital valve is the key to everything," Sturman said.

The primary difference between the Sturman engine and the conventional ICE is that the air is injected rather than drawn into the cylinder on the intake stroke. 

"By injecting rather than drawing the air into the cylinder, we can control the burn rate and temperature of combustion.  This eliminates nitrogen oxide (NOX) emissions by keeping combustion temperatures below 2,000 (degrees Fahrenheit)," Sturman said.   

 
The second major difference is that the Sturman engine retains a small amount of exhaust gas in the combustion chamber on the exhaust stroke to preheat the fuel as it is injected into the combustion chamber on the power stroke. 

"For diesel applications in particular, the preheating effect of the exhaust gas eliminates the need for mechanical vaporization of the fuel by increasing injection pressure," Sturman said.

The next major difference is that, with the valve, fuel, and air timing events of the engine controlled by digital valves, the engine can run in multiple operating modes, such as two, four, six, or eight cycles.  The two-cycle mode can, for example, increase torque by 200 percent because each cylinder produces a power stroke on each crankshaft revolution. 

 
For compression-ignition diesel applications in particular, emissions can be eliminated simply by closing the intake and exhaust valves and compressing the remaining air and fuel in the cylinder through an additional four, six, or eight cycles until the remaining fuel is completely oxidized. 

The extra compression cycles completely eliminate hydrocarbon and carbon monoxide (HC and CO) emissions and can increase fuel economy by as much as 50 percent, Sturman said.

Last, because Sturman's digital valves are fast enough to accurately time valve events at 30,000 crankshaft revolutions per minute, valve lift and timing are infinitely variable.  They can be instantly changed to operate equally well at low- and high-speed operating conditions.

"Flexibility is the most prominent feature of the digitally operated engine," he said.

The 60,000-square-foot Sturman facility employs about 70 people working on three floors.  The top floor is dedicated to management, the second to engineering, and the bottom floor to prototype development and product testing.

The testing facility includes a number of test stations and engine dynamometers.  Electronics are developed in an electronics and computer lab while prototype machine work is performed in a state-of-the-art machine shop facility.

Are the Sturman technologies practical for day-to-day use?  Because Sturman Industries is a consulting, research, and development company that serves such big names as the U.S. Department of Defense, General Motors, John Deere, and Mack Truck, the answer is yes. 

Because Sturman holds more than 80 current patents, Sturman's technology can be found in the designs of many contemporary engines.

Independent repair shops might, for example, be surprised to learn that Sturman's digital-valve technology is used in Ford's diesel-fuel injectors. 

As the demand for increased fuel efficiency and lower exhaust emissions continues, Sturman's digital latching valve might not only be the technology of the here and now but of the future as well.