Fuel for combustion engines has not transformed significantly over the past 100 years, but things may change. Biofuel research continues to advance as off-highway engineers develop new techniques that will let engines run on varying mixtures.
There’s plenty of activity in biofuels, though they trail natural gas in the race to make the leap from alternative energy source to mainstream fuel. U.S. refiners produced around 1.7 billion gallons (6.4 billion L) of biodiesel fuel last year, according to the U.S. EPA. Engine developers throughout the supply chain are working on techniques that let operators run with any mix of fuels on any engine model.
“The adoption of alternative fuels is a calibration issue,” said Bapi Surampudi, Principal Engineer for Engine, Emissions, and Vehicle Research at the Southwest Research Institute. “To minimize cost, the goal has always been to re-use the same electronics in multiple platforms. Therefore, one challenge is to design a common electronic architecture (hardware and software) that works in all cases.”
Researchers are exploring different techniques to efficiently determine the makeup of fuel being used. One strategy is to add sensors that measure fuel in the tank, while another leverages combustion control systems to monitor fuel as it’s fed to the engine.
“For self-propelled vehicles, the detection could be a tank-based analysis and a ‘retune’ or correction method every time the tank is filled,” said Chris Mays, Senior Technical Specialist at BorgWarner’s Advance Engineering Group. “The sensing method could also be continuous. In this case, OEMs need to determine whether to measure the fuel or the combustion. Measuring the combustion, either directly or indirectly, provides the greatest payback as it accounts for engine component and system variation as well as fuel variation.”
The rapid advance in computing power is helping engineer and programmers analyze fuels efficiently.
“Higher performance electronic control units enable a more precise control of the combustion process and reduced penalty efficiency of the alternative fuel engine,” said Ali Maleki, Business Unit Director for Hybrid and Electrical Systems, Ricardo. “New electronic technologies are embedded for better emissions control, gas recirculation control, precise fuel delivery. There is significant trend for alternative fuels in the stationary, railway, and truck applications that are more operating-cost sensitive.”
As control systems evolve and more biofuels move into production, engineers are continuously striving to eke more work from every drop of fuel.
“Engine manufacturers must become knowledgeable of the potential and the drawbacks of different biofuels and gain experience through faster and more sophisticated testing,” Surampudi said.
Much of that knowledge will be gained through modeling and simulation. Combustion is very complex, with major differences arising from minor changes, so many tests must be run to improve efficiency.
“Getting good signals at the sensors is one aspect to consider,” Mays said. “Simulating sensor responses in the design phase can help give good signal-to-noise response. This can include analysis of sensors in the gas flow stream to make sure they are sensing well-mixed gases and are robust to condensate, for example.”