SPRING 2004 — Engine and Emissions
First Fuel Spray Studies Conducted with a Multi-Hole Injector; Fuel Spray Measurements Made at Highest Pressure Yet
CTR researchers recently directed high-brilliance x-rays from Argonne's Advanced Photon Source (APS) into diesel fuel sprays from a valve-covered orifice (VCO)-type multi-hole injector to obtain detailed quantitative data on how injector nozzle structure affects the sprays. Fuel spray characteristics largely determine how fuel burns inside diesel engines, which impacts the production of emissions. A thorough understanding of the effect injector nozzle structure has on the mass distribution and breakup properties of sprays is therefore key to designing injectors that maximize fuel efficiency while minimizing particulate and nitrogen oxide (NOx) emissions.
Previous work by the research group focused on single-hole nozzles, which are used primarily by engine research laboratories. The Bosch VCO-type multi-hole injector, on the other hand, is very similar to those inside modern diesel engines. Its use, therefore, represents an important milestone toward the goal of directly measuring the mass distributions of fuel sprays found inside actual engines. The high-brilliance x-rays of the APS permit such measurements even in the crucial near-nozzle region, which cannot be investigated with laser-based optical techniques.
This first experiment with a multi-hole injector was done in collaboration with scientists at General Motors Corp. and the University of Wisconsin and was conducted at ambient temperature and pressure. Two nozzles having different internal structures were involved. The next step will be to map the mass distributions of fuel sprays as they enter a pressurized environment to simulate conditions inside an engine cylinder more closely.
The data being generated by the research group will help in developing more accurate fuel spray models. Current spray models are unable to accurately predict the mass distributions and breakup processes of diesel fuel sprays even when all of the parameters governing the sprays are known. The mass distribution data obtained by the group will enable modelers to make quantitative comparisons with the predictions of their models, thereby helping them improve their performance. More accurate spray models will reduce the amount of trial-and-error work that manufacturers must perform in designing engines that are more fuel efficient and produce less pollution.
The multi-hole injector work adds a new dimension to the group's continuing research with single-hole fuel injectors. CTR researchers recently conducted the first complete mass distribution mapping measurements at a pressure of 10 bar, which extends the research they previously conducted at ambient and 5-bar pressures. Such work has already proved valuable to researchers at Michigan Tech University, who have begun using it to fine-tune their computational models.
An important factor in conducting fuel spray experiments at high pressures involves the diesel fuel additives that are needed to increase the contrast of fuel spray images. Spray measurements at high ambient pressures require a shift in x-ray wavelength regime because the long wavelength x-rays used at low pressures are easily blocked by pressurized gases. The change to shorter x-ray wavelengths will enable the x-rays to penetrate the pressurized gases, but will require finding a new fuel additive that is sensitive in this wavelength regime, as the additives work well only over a narrow range of x-ray wavelengths. The researchers continue to test promising candidates.
X-ray images of the mass distributions of fuel sprays from nozzles having different internal structures. Computer-based spray models attempt to predict a fuel spray's mass distribution based on the internal structure of the injector nozzle. Quantitative measurements such as these, available for the first time, can help to fine-tune these models.
Sponsor
U.S. Department of Energy Office of Energy Efficiency and Renewable Energy in collaboration with General Motors Corp. and the University of Wisconsin.
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