The purpose of this paper is to describe a novel liquid fuel
conditioning process that is incorporated within a 4-stroke
internal combustion engine. The process takes place inside a small
external vaporization chamber linked to the engine cylinder. A
vaporization chamber transfer port is located adjacent to the
cylinder bottom dead center. After an injected primary liquid fuel
has evaporated and superheated inside the vaporization chamber it
is transferred into the cylinder near the end of the intake stroke
to form a homogenous mixture with a fresh air charge. Combustion is
triggered by compression-ignition of a pilot fuel spray. Near the
end of the expansion stroke, hot combustion products enter the
vaporization chamber via the vaporization chamber transfer port.
Thereafter, those products are entrapped inside the vaporization
chamber during about 320° of crankshaft rotation since the
vaporization chamber transfer port is sealed by the piston skirt
for part 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 stroke.
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 gasoline fuel droplets of 180 micron 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 aftertreatment 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.
