Injecting diesel fuel or oil through port injection for upper cylinder lubrication in opposed-piston, two-stroke diesel engines

Title of Invention:
Port Injection for Upper Cylinder Lubrication

Name of Inventor or Inventors:
Michael Tebbe

Date of Disclosure:
May 14, 2012

Background:
Piston ring and cylinder wear is a common concern in two-stroke engines, especially in the location of compression rings linear reversals. These reversals occur at top dead center (TDC) and bottom dead center (BDC) in the cycle. This particular invention is focused on the TDC center 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:
Using a standard automotive fuel or oil injector located in the intake port tubing leading to the engine block port area, this invention can be explained as follows:

  • If diesel fuel is used as the desired lubricant through port injection, the injector will provide a small volume of fuel, through the intake port, late in the charge motion scavenging on the compression phase of the cycle. The timing and volume of fuel will vary due to exhaust crank phasing, transport timing, engine speed and engine load. This volume of fuel will provide upper-cylinder lubricant to lubricate the compression rings, piston skirt and cylinder wall through the engineered swirl effects induced by the intake port geometry (see below). A possible secondary usage for this port injection would be to provide a pilot charge to the combustion process to aid in the performance and emissions process. This would increase the volume of fuel through the intake port such that after the “wall-wetting” process, there will remain enough residual fuel to support the pilot combustion. That being said, 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.
  • If oil is desired as the lubricant through port injection, the injector will provide a small volume of oil, through the intake port, late in the charge motion scavenging on the compression phase of the cycle. The timing and volume of oil will vary due to exhaust crank phasing, transport timing, engine speed and loads. This volume of oil will provide upper-cylinder lubricant to lubricate the compression rings, piston skirt and cylinder wall through the engineered swirl effects induced by the intake port geometry. A common two-stroke oil can be used. Two-stroke oils are ashless and contain zero phosphorus. This is highly desired for optimal diesel catalyst and DPF function.

This oil injection method does provide a vast majority opportunity for companies to work with oil manufacturers to develop an oil formula for upper cylinder lubrication. The oil formula can contain special ashless modifiers for reduced friction, ashless additives for neutralizing varnish in the piston grooves, and ashless additives for anti-oxidation and corrosion projection.