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SONEX Low Soot Diesel Design (LSDD)
The Sonex Combustion System (SCS) improves the combustion of fuels in four-stroke, direct injected (DI) engines through design modification of the pistons to achieve chemical/turbulent enhancement of combustion. Sonex U.S. Patents No. 5,862,788 (January 1999) and No. 6,178,942 B1 (January 2001) address a combustion chamber for non-spark ignition, DI engines that improves the process of combustion through a combination of chemical and fluid dynamic effects. These effects are enabled by the patented piston technology as shown schematically in the figure below.
CROSS SECTION of SONEX LSDD PISTON
SCS DI technology embeds uniquely shaped cavities called micro-chambers (MCs) into the piston around the circumference of the piston bowl. These MCs thus form a segmented ring around the piston bowl, with each micro-chamber positioned in line with a fuel injector spray. The MCs are connected to the piston bowl by tunnel-like vents arranged strategically so that a small fraction of the fuel can be trapped in the MC. The flame from the main chamber is quenched by the vent, preventing complete combustion in the MCs. Only slow and incomplete oxidation (of the trapped fuel) takes place, resulting in the formation of highly reactive radicals and intermediate species. These materials exiting at high velocity are very effective in reducing emissions in standard diesel engines; they also provide the means to achieve controlled auto-ignition at low/moderate compression ratios with a variation in the basic SCS design.
The Sonex DI technology is applicable over two distinctive paths. The first path, the Low Soot Diesel Design (LSDD), enables soot and oxides of nitrogen (NOx) reductions in standard DI diesel engines at compression ratios greater than 16:1. The second design path, called Sonex Controlled Auto Ignition (SCAI), is for low/moderate compression (<12.5:1) DI engines to enable fully controlled auto-ignition and combustion with single phase high rates of heat release for a variety of fuels. SCAI “spark-less” combustion in un-throttled, DI lightweight engines reduces emissions and increases fuel economy as shown in a separate section.
In the LSDD the emphasis is in placing the vent (with its high velocity jet) for maximum interaction with the soot cloud. During the power stroke, the pressure drops in the combustion chamber more rapidly than in the MCs, and highly reactive gases are expelled from the MC at high speeds into the soot cloud. In addition, the soot level remains at a reduced level when high levels of exhaust gas recirculation (EGR) are used to reduce NOx. The LSDD has been shown to be completely different and more effective than an air cell. Sonex LSDD experience with multi-cylinder turbo-charged engines shows an overall cycle soot reduction of 50% and an accompanied 10% reduction in NOx (without EGR). Significant reductions in NOx can be achieved with common rail control of injection timing and EGR while holding the soot level at the reduced level. Ricardo Consulting Engineers in Europe presented results of their evaluation of a major OEM engine with pre-production LSDD pistons, a computation fluid dynamic (CFD) and gas dynamic analysis at the SAE Fuel and Lubes, May 2002 Conference: SAE 2002-01-1682.
Fundamentals of LSDD
l LSDD is at “Standard” Diesel Compression ratio and consists of a piston with Micro-chambers (MC)
· One MC/Injector Spray
l One Vent/MC is located to receive a lean charge during injection
l Jets from MC Create High Turbulence During Expansion of the Charge. Expansion is Faster in the Combustion Bowl so Pressure is Lower
What happens during Expansion???
l LSDD MC Vent is Located to Allow High Velocity Jet to Interact with Average Location of Soot Cloud in the combustion bowl, destroying the Soot
l Computational Fluid Dynamics (CFD) has been used to show this as given below:
Note the Bisecting of the Red Soot Cloud and its Destruction in the far right column
FROM (SAE 2002-01-1682)
FROM (SAE 2002-01-1682)
Use of the proper injection timing shows significant soot reduction, regardless of speed or load (including idle) as shown in the graph below (from SAE 2002-01-1682). At 75% Load at the engine rpm of peak torque, soot reduction was nearly 90%. Although there is an 18% reduction in Soot at Idle, the injection system timing would have to be optimized for idle rpm for even more soot reduction.
SCS LOW SOOT DIESEL DESIGN SUMMARY
l CAN REDUCE SOOT AT ALL OPERATING POINTS BY UP TO ~90% WITH PROPER INJECTION TIMING
l REDUCE SOOT WITH OR WITHOUT EGR (TO REDUCE NOx)
l WITH FUEL CONSUMPTION EQUIVALENT TO BASELINE ENGINE
Two sample pre-production Sonex LSDD pistons are shown below for the engine reported on in the SAE article. The first is a composite with the upper half produced by powder metallurgy, the lower half attached by squeeze cast aluminum. The second is all aluminum with the upper section containing the micro-chambers attached by electron beam welding. Both pistons were produced by Federal Mogul for a European OEM. Simplified fabrication techniques enabling production on current piston lines are now being developed.
SONEX RESEARCH, INC.
23 Hudson Street, Annapolis, MD 21401
Tel: 410-266-5556; Fax: 410-266-5653
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