Fuels Research

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Fuel composition can have a profound impact on the performance of direct-injection (DI) diesel engines, such as soot emissions, cold-start characteristics, and compatibility with exhaust-gas aftertreatment systems. For instance, the addition of oxygen-containing compounds ("oxygenates") to diesel fuel can dramatically lower soot emissions. Past research conducted at the CRF has shown that an oxygenate's molecular structure can have a significant impact on its ability to eliminate soot.

Fuel formulation is especially important for new engines that will operate in low-temperature combustion (LTC) regimes because chemical-kinetic processes that are strongly dependent on fuel type largely control the limiting processes of ignition and heat release rate. LTC modes such as homogeneous charge compression ignition (HCCI) are of considerable interest because they can simultaneously reduce NOx and soot emissions by two orders of magnitude while maintaining high thermal efficiency. Currently, however, LTC can be achieved only over a limited portion of an engine's typical operating range.

Our research is focused on developing a fundamental understanding of the combustion characteristics of advanced liquid petroleum-based, bio-derived, and synthetic fuels, and applying this knowledge to:

• Expand the LTC operating range through the use of new fuels and/or combustion systems
• Improve DI diesel combustion performance where LTC operation is not possible (e.g., at high power density)
• Enhance energy security and minimize greenhouse-gas emissions by enabling the use of non-traditional and renewable fuels

The Fuels Research Laboratory is built around the Sandia Compression-Ignition Optical Research Engine (SCORE). The SCORE is a single-cylinder version of a Caterpillar® C 10 engine that has been modified at Sandia to provide extensive optical access into the combustion chamber (see schematic). The optical engine has a bore of 125 mm, a stroke of 140 mm, and a displacement of 1.72 liters. It uses a HEUI® fuel injector that is capable of injection pressures in excess of 140 MPa. Considerable design and development work has been done to enable the precise control of important operating parameters to ensure exceptional experiment repeatability.

Advanced laser and imaging diagnostic techniques are used to observe combustion and emissions-formation processes through windows in the piston and the upper periphery of the cylinder liner. Detailed analysis of the in-cylinder measurements, coupled with engine-out emissions data, help expand the understanding of exactly how and why pollutants are formed so that they can be minimized. The fuels research project facilitates efficient and rapid progress toward the commercialization of optimal fuel and engine technologies through publication of research results in the open literature and through close collaborations with engine manufacturers, energy companies, other government laboratories, and academia.