Technician Jerome Cherel sets up an experiment on the optical engine, which shows the quartz cylinder liner and piston.

    Using quartz and sapphire components, high-powered lasers, and scientific cameras researchers are able to see inside an operating engine, and that vision is proving to be a valuable aid for finding ways
to reduce diesel emissions.

        “We can use the optical engine as a tool to get visual data, to get quantitative data, and to better understand the physical processes that are occurring in a standard metal engine,” said Julian Kashdan, Research Engineer in the EnergyApplication Techniques Division at IFP (French Institute of Petroleum) in Rueil-Malmaison, France.

    An optical engine—essentially akin to a standard, all-metal engine but with certain parts fashioned in quartz and sapphire—has been a part of the research community since the 1980s. The transparent engine of today, however, is serving a vital role in the development of greener diesel engines.

Looking inside the combustion chamber of the optical engine via a 45° mirror, which is housed inside an extended piston. The bluish light corresponds to combustion luminosity.

“We’re trying to solve the NOx and soot emissions problem with diesel engines using low-temperature combustion strategies, and so we want to understand what’s happening in-cylinder,” said Kashdan. In one set of tests currently being conducted in the engine laboratory, an optical diesel engine is fitted with a quartz cylinder and quartz piston bowl. “Using laserspectroscopy techniques, we are able to visualize the physical processes occurring in-cylinder,” Kashdan said.

    Researchers can observe a range of operating conditions, including the time span from the injection of fuel into the cylinder on through engine combustion. “This is very important because it has a big effect on emissions formation. The data that we obtain is useful in terms of understanding what is happening physically so that we can try to optimize the designs of the combustion chamber. We can also provide this important data to the numerical modelers—meaning the people who perform CFD calculations for three-dimensional simulations. The data also can be used to validate those models,” said Kashdan

A full view of a single-cylinder diesel optical
research engine within the IFP engine lab.

    In the past few years, the homogeneous- charge compression-ignition (HCCI) diesel engine has received optical attention. “In order to get an HCCI diesel engine on the market, we need to look at increasing the low-load operating range limitation in order to really maximize the benefits of low-temperature diesel combustion. But when combustion temperatures are reduced, hydrocarbon and carbon
monoxide emissions are problematic, which is why it is so important to see and understand what is happening in-cylinder in order to get to the source of the problem,” Kashdan said.

    Information gleaned from optical engines and other forms of analysis techniques are valuable discovery tools for companies involved with diesel technology. For instance, Delphi has been involved with diesel fuel injection technology for 50-plus years, and new products are always on the road map. “Compared to today’s diesel engines, the injection nozzle that would be used in conjunction
with an HCCI engine might need to have a larger number of holes. It could also have different spray angles, smaller hole size, and a more sophisticated injection pattern, which is why Delphi engineers are helping IFP researchers interpret what will be needed,” said Pascal Dutfoy, Strategy and Planning Director for Diesel at Delphi’s Powertrain Division in Blois, France.
                                                     Kami Buchholz