Chemical engineers at the University of California, Riverside, have developed a unique liquid fuel that requires an electric current to ignite. Unlike traditional fuels, this innovative fuel does not react to flames or cause accidental fires during storage or transportation, making it a "safe" liquid fuel.
"The fuel we usually use is not very safe. It can ignite after it evaporates, and it's difficult to prevent that from happening," said Yujie Wang, a UCR chemical engineering doctoral student and co-author of a new paper on this fuel. "When fuel burns, it's not the liquid itself that's burning. Instead, it's the volatile fuel molecules hovering above the liquid that are ignited when they come into contact with oxygen and flame. Removing the source of oxygen can extinguish the flame, but that's difficult to do outside the engine. If you throw a match into a pool of gasoline on the ground, what's burning is the vapor of the gasoline. You can smell the vapor and know right away that it's volatile, and if you can control the vapor, you can control whether the fuel burns."
The Journal of the American Chemical Society paper describes how the team created the fuel, and more technical details are included in their patent application.
The basis of the new fuel is ionic liquids, which are liquefied salts. "It's similar to the salt we use to flavor food, which is sodium chloride. The salt we used in this project has a lower melting point than table salt, a lower vapor pressure, and it's organic," Wang said.
Once in the lab, the team modified the ionic liquid's recipe to replace the chlorine with perchlorate. They then ignited the liquid with a lighter, which is hot enough that if it were to burn, it would.
Next, the team tried applying a voltage and then igniting it with a lighter flame. It actually ignited, and once the current was turned off, the flame disappeared. They were then able to repeat the process over and over again - applying voltage, seeing smoke, igniting the smoke to make it burn, and then turning off the current, giving the fuel a rapid start-up and stop system.
Adding more voltage to a liquid creates a larger flame that outputs more energy. Therefore, this method can also function like a metering or throttling system in an engine.
"Combustion can be measured this way, and cutting off the voltage acts like a dead man's switch - a safety feature that automatically shuts down the machine if the operator becomes incapacitated," said Michael Zachariah, distinguished professor of chemical engineering at UCLA and corresponding author of the paper.
In theory, ionic liquid fuel could be used in any type of vehicle. However, there are still some questions that need to be answered before commercialization can be achieved. The fuel needs to be tested in various engine types and its efficiency needs to be determined.
"One of the interesting properties of ionic liquids is that they can be mixed with conventional fuels and still maintain their properties," Zakaria said. "But more research is needed to understand what proportions of ionic liquids can be mixed and made non-flammable."
Although there are many aspects of the liquid that need to be further explored, the team is pleased to have been able to create a fuel that is safe and avoids accidental, accidental fires.
"It will definitely be more expensive than the current way of producing fuels. These compounds are not usually produced in batches, but if they were, the cost would be reduced," Zakaria said. "How competitive is that? I don't know. But if safety is important, this is one of the major aspects. If you make a safe product, there are benefits beyond the bottom line."