Diesel pre-charge for upper cylinder lubrication in opposed-piston, two-stroke diesel engines

Title of Invention:
Diesel Pre-Charge for Upper Cylinder Lubrication

Name of Inventor or Inventors:
Michael Tebbe

Date of Disclosure:
February 9, 2012

Background:
Cylinder wear in the location of compression rings linear reversals is a common concern with opposed-piston, two-stroke diesel engines. These reversals occur at top dead center (TDC) and bottom dead center (BDC) in the cycle. This particular invention, however, is focused on the TDC reversal location.

In four-stroke engines, the TDC ring reversal area is lubricated by rings scraping oil up the cylinder with no interruption in the cylinder bore. However, opposed-piston, two-stroke diesel engines have intake and exhaust port features in the bore that interrupt and prevent the possibility of the rings scraping, or transporting, oil past the port features—linearly up the cylinder—to the critical ring reversal areas. The lubrication, in this location of the cylinder, is critical to ensuring the sealing, durability, longevity and power demands of the opposed-piston, two-stroke diesel engine. Engine oil consumption is also a concern with opposed-piston engines. However, with maximum oil control, the upper cylinder will lack the lubrication for engine longevity and durability.

Novelty:
The only lubrication methods currently used are expensive cylinder or ring coatings, circumferential striations or accumulator grooves in the liner or piston. While cylinder or ring coatings can be effective, the cost standards for high-volume production render this method undesirable. The same is true for accumulator grooves, which also have undesirable cost standards.

Invention:
The invention uses the existing diesel injectors to provide a small volume of fuel roughly concurrent to the time when the piston closes the exhaust port on the compression phase of the cycle, which can occur earlier in the cycle if transport delay is utilized. This volume of fuel will provide upper-cylinder lubricant to lubricate the compression rings, piston skirt and cylinder wall, and it will be less than the amount required for combustion.

There exists opposition to the argument of “wall wetting” by engine fuel. Even so, the system presented includes optimized oil control for reduced/minimal ash contribution to cycle emissions. Wall wetting is a problem if the fuel is very hot and evaporates lubricant off of the cylinder walls. With this proposal, the fuel is relatively cold due to the injection occurring while the cylinder pressure is very low. Research has shown that diesel fuel exhibits nearly identical lubricous properties to common 15W-40 engine oil. The concept of utilizing a consumable and native liquid may increase the hydrocarbon emission output. However, unlike ash, hydrocarbons can be minimized or eliminated by standard diesel oxidation catalyst. The invention presented will replace oil lubrication in the upper cylinder with a small volume of consumable diesel fuel. The efforts are concentrated on maintaining or reducing the emission components with the introduction of the pre-charge.