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Sturman Electro-Hydraulic Valvetrain Exceeds 40% Peak Efficiency in NG Engines
In brief: Sturman Industries has been developing a process called Hydraulic Valve Actuation since 1995 and says they are now showing a 40% efficiency increase in natural gas engines with an accompanying 18% reduction in fuel consumption.
The technology uses electro-hydraulic valves rather than a camshaft to achieve these gains. In spark-ignited natural gas (NG, methane) engines, which are usually meant to replace diesel, more fuel or less performance is expected in comparison to the diesel fuel equivalent.
With this new set of technologies, however, Sturman says that this maxim (less efficiency or less performance) is no longer valid.
The latest round of work was funded by a $1 million grant from the California Energy Commission and was tested on one of the industry's most prominent 15-liter heavy-duty diesel engine platforms, used in both transportation and power generation.
One of the problems with these engines that are often under continual, but not maximum load, is that they often have very low emissions but sacrifice efficiency to get that. The expensive after-market treatments for diesel are the most common reason for this loss. With natural gas, of course, those treatments are unnecessary but the efficiency loss was still there.
"It was clear we had to combine the best attributes of each approach, so we chose to apply our Hydraulic Valve Actuation system to eliminate the throttling losses, with a simple three way catalyst to clean up remaining emissions. The camless engine combines the benefits of Lean-Burn and Stoichiometric Natural Gas Engines." —Miguel Raimao, responsible for Business Development at Sturman
For testing, the stock production diesel engine was fitted with a commercially-available natural gas fuel system along with Sturman's HVA. The HVA controls valve train timing via electronics and gives full, independent control of valve timing, duration and de-activation. Stock turbocharging and EGR systems were left in place.
The control over valves allowed a compression ratio increase from 10:1 to 14:1 and also allowed for control over how many valves were actually in operation - under part load, the engine was reduced to operating on only 3 valves, increasing efficiency greatly.
And so ...
That amount of control is what gives the Sturman HVA system its huge efficiency gains, especially under partial loads as is common in power generation and on-road cruising in large trucks.
Photo credits: Sturman
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