Researchers from the U.S. Department of Energy’s Argonne National Laboratory are using particle accelerators as well as X-ray vision to understand how a fuel spray works within a fuel injection system. The findings could potentially be an eye opener in assessing how modern car engines work, which the scientists hope will help find cleaner, more efficient ways of burning petrol and diesel.
Fuel injection has been the subject of research for more than 20 years; however the physics of sprays are still not very well understood. Basic discoveries still need to be made. Now in order to try shed some light on the matter, the Argonne researchers have turned to a smaller version of the Large Hadron Collider to see if it can help reveal details about fuel injection that haven’t been seen before.
Dr Christopher Powell, an engine research scientist at Argonne’s Sector 7 lab, is investigating the precise details of what happens when fuel injection systems squirt petrol or diesel into the cylinders which house the pistons that drive internal combustion engines. It’s a process that lasts around one millisecond and occurs many times a second in a running engine. Understanding how the fuel is dispersed and mixed when this happens is crucial to making the burning process as efficient as possible.
The high energy X-rays Powell uses in the experiment exit the particle accelerator through a hatch before travelling along a steel pipe, being focused and then beamed into a model of a cylinder. A variety of injectors can be used, from standard ones used in today’s cars to experimental designs.
This process allows the flow of droplets of fuel to be imaged in a way that is not possible with ordinary light or lasers, for example. Using visible light presents challenges similar to those of using car headlights in fog, which consists of droplets of water suspended in the air, just like a jet of fuel sprayed from an injector.
Visible light can highlight the outline of fuel spray but not any internal detail. X-rays, on the other hand, can pass through the relatively large droplets of fuel because their wavelength is much shorter than that of visible light. On a much smaller scale, some of the X-rays are absorbed by the atoms that make up the drops, making high-resolution imaging possible. “If you count how many X-rays are absorbed, you can count how many atoms there are,” Powell explains.
The result is a detailed moving image of a jet of fuel in the cylinder that can be presented in various ways, in black and white or in color. A close-up of the fuel injector X-ray revealed individual components in action, with the valve moving to release the high-pressure fuel. Bubbles can be seen in the fuel supply. Powell says their presence was unknown until identified recently using this high-energy X-ray imaging technique.
“That was something interesting we discovered just a few months ago,” asserts Powell. “When the injector valve closes, gas is actually pulled back inside the injector. This is important for quality issues for an injector.”
In a real engine the gas in the cylinder being pulled back into the injector is likely to be made up of hot combustion products, which could be corrosive. Manufacturers are looking at these findings to see what impact this process could be having on the life spans of their injectors.
