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The method for supercritical diesel combustion of the present invention combines fumigation and supercritical diesel fuel combustion to effect greater fuel efficiency and reduce exhaust gas pollutants from a compression ignition engine such as a diesel engine. This pre-combustion of the fumigant gases combined with the engine's compression of the combustion chamber gases is managed to attain a supercritical combustion chamber environment into which the liquid diesel fuel is injected. This targeted supercritical combustion chamber environment causes the diesel fuel to become a supercritical fluid prior to combustion, resulting in significantly greater efficiency and negligible exhaust gas pollutants resulting from the combustion of the diesel fuel.
Fumigation of a diesel engine air intake charge with a combustible gaseous fuel has always required that the injected liquid diesel fuel be the pilot ignition source initiating the combustion event. This allowed for accurate timing of the combustion event, reduction of the total diesel fuel consumed, and reduction of exhaust gas pollutants because the gaseous fuel combusts much more completely than the liquid diesel fuel.
Combustion of diesel fuel as a supercritical fluid causes the combustion event to resemble a gaseous fuel combustion event. As a supercritical fluid diesel fuel does not exhibit surface tension and has a diffusion two magnitudes greater than as a liquid. These are the two main properties of a supercritical fluid which contribute to greater combustion efficiency and lower exhaust gas pollutants.
Liquid diesel fuel is injected into the combustion chamber by very high pressure to effect atomization of this liquid fuel. The result is a spray composed of droplet and ligaments entering into the combustion chamber environment. There is an ignition delay time period as the liquid fuel droplets and ligaments take on heat from the combustion chamber gases and commence to vaporize. It is this diesel fuel vapor which combusts. Diesel combustion is generally considered to be a lean combustion event but this is only true when looking at the bulk number relationship for the fuel and the oxidant. Each droplet and ligament creates a very fuel rich combustion zone surrounding their surface. These rich combustion zones create “prompt” NOx (nitrogen compounds formed during elevated temperature combustion events and during fuel rich combustion) and encapsulate the remaining liquid within the droplet or ligament in a zone of extreme heat which creates pyrolysis and coking of the remaining fluid. The source of particulates in the exhaust gas and temperature created NOx.
As a supercritical fluid diesel fuel does not exhibit surface tension, therefore droplets and ligaments cannot form, or if formed cannot remain formed. This excludes the possibility of fuel rich combustion zones, reducing the production of both prompt and thermal NOx as well as the pyrolysis and coking of the diesel fuel.
The companion effect of the loss of surface tension is that the diesel fuel now has 100 times greater diffusivity than as a liquid droplet or ligament. The combustion effect is that the diesel fuel is now at least 100 times more in contact with the oxidant. The result is a combustion event that releases more heat energy in a shorter period of time than a typical diesel combustion without the formation of prompt NOx and particulates.
It is therefore an object of the present invention to provide a new and improved supercritical combustion chamber environment for compression ignition engines such as diesel engines.
It is another object of the present invention to provide a diesel engine combustion chamber environment with improved fuel efficiency.
A further object or feature of the present invention is a diesel engine combustion chamber environment with reduced NOx and soot emissions.
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