Liquid Fuel Vaporization Process Built Inside 2-Stroke Piston Engines 2012-36-0122
The purpose of this paper is to describe a novel liquid fuel conditioning process incorporated within a 2-stroke internal combustion engine. The process takes place inside a small vaporization chamber integrated within the engine piston. The vaporization chamber inlet/outlet is located on the piston skirt. After an injected liquid fuel has evaporated and superheated inside the vaporization chamber, it is transferred into the cylinder to form a homogenous mixture with a fresh air charge. Combustion is triggered by compression-ignition of a pilot fuel spray. After combustion completion, hot combustion products enter the vaporization chamber via a transfer port formed in the cylinder wall. Thereafter, those products are entrapped inside the vaporization chamber with the inlet/outlet aperture sealed by the cylinder wall for a portion of the cycle.
Unlike spark ignition, compression ignition or homogeneous charge compression ignition engines, here the liquid fuel is injected into the vaporization chamber during the expansion phase of a preceding cycle. Fuel droplets absorb heat from the hot entrapped combustion products and vaporization chamber walls, where they evaporate and reach a superheated gaseous state. Calculations predict that the residence time available inside a typical vaporization chamber of an engine running at 6,000 RPM is sufficient to evaporate and superheat diesel fuel droplets larger than 180 microns SMD.
It is anticipated that this novel concept could substantially reduce the untreated emission levels of nitrogen oxides, carbon monoxide, particulate matter and unburned hydrocarbons when compared to spark ignition, compression ignition or homogeneous charge compression ignition engines. This projection implies that less costly and simpler after-treatment devices will suffice to comply with emission standard regulations.
An improvement in engine fuel economy is expected because: (1) relatively high design compression ratio, (2) un-throttled operation and (3) faster heat release rate than that corresponding to either spark ignition or compression ignition engines.
The combustion process prevents detonation and diesel knocking therefore the fuel does not need to be rated for octane or cetane number. These features allow this engine to efficiently employ gasoline or diesel fuels without additives or blends. Additionally, the system is expected to effectively utilize low-cost petroleum derived fuel, biodiesel, bio-alcohol, vegetable oil, and in special applications, coal-water-slurry fuels.