Dimethyl ether (DME) enhanced gasoline engine

Abstract

An engine having DME pilot ignition is disclosed. DME Pilot ignition creates far more energy than a conventional spark plug, thus minimizes the possibility of misfire in the engine map. DME injection can be used in a number of ways. In one embodiment, DME injection replaces the conventional spark plug in an Otto cycle engine. In another embodiment, DME injection is used in addition to spark ignition to minimize the use of DME. In this embodiment, DME injection is only used during those portions of the engine map where misfire may occur, or during those times when a misfire sensor detects misfire. DME injection can also be used in conjunction with alcohol boosting in other embodiments.

Description

[0001]This application claims priority of U.S. Provisional Application Ser. No. 61 / 169,841, filed Apr. 16, 2009, the disclosure of which is incorporated herein by reference in its entirety.BACKGROUND[0002]Spark ignited engines face multiple constraints in operation that limit their efficiency. Two such limitations are misfire and knock. Misfire is the phenomenon whereby the gasoline-air mixture does not ignite in the presence of a spark. Knock is the uncontrolled auto-ignition of the unburned air-fuel mixture during the combustion process.[0003]Lean operation, which is defined as operation in which there is an excess amount of air for the amount of fuel introduced, has been known to increase the efficiency of an engine through the reduction of frictional losses, as well as decreased heat losses to the cylinder wall due to lower combustion temperatures. The NOx emissions decrease when excess amounts of air are used, and it is possible to decrease NOx emissions to the point where ther...

AI Technical Summary

Benefits of technology

[0010]The problems of the prior art are overcome by the present system and method, which discloses an engine having DME pilot-spark ignition. DME-spark pilot ignition creates far more energy than a conventional spark plug, thus minimizes the possibility of misfire in the engine map. DME injection can be used in a number of ways. In one embodiment, DME injection replaces the conventional spark plug in an Otto cycle engine, which depends on flame propagation. In another embodiment, DME injection is used in addition to spark ignition to minimize the use of DME. In this embodiment, DME injection is only used during those portions of the engine map where misfire may occur, or during those times when a misfire sensor detects misfire. DME injection can also be used in conjunction with alcohol boosting in other embodiments.

Problems solved by technology

Spark ignited engines face multiple constraints in operation that limit their efficiency.

Two such limitations are misfire and knock.

Knock is the uncontrolled auto-ignition of the unburned air-fuel mixture during the combustion process.

However, in general, this requires an air to fuel ratio that is so great that combustion stability (i.e. cycle-to-cycle variation) suffers, thereby resulting in misfire.

In addition to misfire, the second limitation of spark ignited engines is knock, the uncontrolled auto-ignition of the unburned air-fuel mixture during the combustion process.

Thus, knock places severe limitations on the use of high compression ratio, and turbocharging, which limits the potential efficiency of the engine.

However, where there is high dilution (either through very lean operation or heavy EGR), reliable ignition of the mixture may be compromised.

However, the use of conventional liquid diesel fuel as a pilot fuel in an Otto cycle engine is problematic.

Also, providing enough excess air to eliminate soot generation is an unattractive solution because, in a given engine, excess air means less fuel is combusted, and therefore less power is produced.

Even more important, excess oxygen in the exhaust makes it impractical to use the conventional, efficient and economical 3-way catalysts commonly used to clean the exhaust of stoichiometrically fueled spark ignition engines.

Therefore, expensive and inefficient diesel exhaust catalyst systems would need to be employed if conventional diesel fuels were to be used as pilot fuel.

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