Fuel formulations to extend the lean limit (law770)

Details Fuel formulations to extend the lean limit (law770) Fuel formulations to extend the lean limit (law770)

1999-02-12

2001-03-27

McAvoy, Ellen M. (Department: 1764)

Fuel and related compositions

Liquid fuels

Organic oxygen compound containing

C044S447000, C044S448000

Reexamination Certificate

active

06206940

ABSTRACT:

FIELD OF THE INVENTION
The invention is related to fuels for extending the lean burn limit in internal combustion engines. More particularly, the invention is directed towards fuels containing at least one species having a high laminar flame speed and specific distillation characteristics. The fuel permits operation of lean burn engines at lower lean burn limits resulting in fuel economy gains and emissions reduction.
BACKGROUND
One of the most important recent advances in spark ignition engines involves operation under lean conditions at low to moderate load to achieve fuel economy gains. Significant technological developments have been made in engine design and configuration to facilitate operation under lean conditions. Spark ignition engines are capable of operating with known fuels at a normalized fuel to air ratio (“&PHgr;”) below 1.0. The normalized fuel to air ratio is the actual fuel to air ratio divided by the stoichiometric fuel to air ratio. The &PHgr; at which an engine begins to exhibit unacceptable torque fluctuations is called the “lean limit”. Still further fuel economy improvement in such engines may be achieved and NO
x
emissions reduced by operating the engine with a fuel capable of extending the engine's lean limit.
Fuel economy gains in these lean burn engines are typically realized during operation at low and moderate load; however at high load, these engines operate at a &PHgr; of about 1, requiring that the fuel meet octane and other standard fuel specifications. Accordingly, to have practical application, the fuel of the present invention must meet octane and other standard fuel specifications.
Cold engine startup is a known source of problematic engine emissions. Spark injected (“SI”) engines, lean burn or conventional, effectively operate under partially lean conditions during cold startup because of incomplete fuel vaporization. Lean limit improvements during cold engine start up would beneficially lower hydrocarbon emissions by reducing the fueling requirement for effective combustion.
There is therefore a need for a fuel that meets standard fuel specifications and is capable of extending the lean limit of engines. The fuel of this invention meets these needs.
SUMMARY OF THE INVENTION
In one embodiment, the invention is a fuel comprising an effective amount of at least one species having a laminar flame speed greater than isooctane's laminar flame speed, laminar flame speed being measured at a &PHgr; ranging from about 0.4 to about 0.8, and fuel distillation/volatility characteristics including: T
50
less than about 77° C. Final Boiling Point less than about 160° C., Initial Boiling Point greater than about 32° C. In another embodiment, the invention is a method for reducing &PHgr; in a liquid fueled, port-injected engine without increasing torque fluctuations. The invention may concurrently reduce NO
x
by allowing the engine to operate at a lower lean limit.
The high laminar flame speed species of the present invention may be selected from the group consisting of
 R1—O—R2, R1—C═C—R2,
and mixtures thereof, wherein R1, R2, R3, R4, R5, and R6 are independently selected from the group consisting of H, linear, branched, cyclo alkyl, and aryl or alkyl aryl, provided that the species has a total number of carbon atoms ranging from about 5 to about 12, and provided that when the species is
R1—O—R2
that both R1 and R2 are hydrocarbyl and the total number of carbon atoms in the species ranges from about 7 to about 12.
In still another embodiment, the invention is a fuel for use in a port fuel-injected engine with a &PHgr; ranging under low load conditions from about 0.4 to about 0.8 and with torque fluctuations less than about 0.6 N-m.


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