HCCI: Homogeneous Charge Compression Ignition Engines
07-23-2006, 03:12 PM
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Suzuka Master
Thread Starter
HCCI: Homogeneous Charge Compression Ignition Engines
I haven't heard of this type of engine before so I tought it might be worth posting the details.
July 16, 2006
Green Tech
A Well-Bred Engine Carries Best Genes of Its Parents
By KEVIN CAMERON
NO combustion process for converting fuel to forward motion is perfect. Though engineers can choose from a selection of combustion processes that have been developed for use in today’s automotive engines, each has some shortcoming — in efficiency, cost or environmental friendliness — that must be weighed against its benefits.
Gasoline engines, for instance, can be designed for very low exhaust emissions, but may leave something to be desired in efficiency. Small diesel engines can return terrific fuel economy, but they are costly, and scrubbing their exhaust gases to meet environmental regulations is a big challenge.
Often, the disadvantages that follow the “but” overwhelm the gains.
No wonder engineers are looking for new ways to combine the pluses of different engine types. One operating cycle for engines under wide study in the industry, known as Homogeneous Charge Compression Ignition, cherry-picks the best traits from gasoline and diesel designs — low emissions and high efficiency, respectively.
The H.C.C.I. engine runs ideally as a combination of the two. Like a spark-ignition engine, its fuel enters the cylinder premixed with air. The fuel is evenly distributed in the air — not concentrated around the fuel injection nozzle — accounting for the homogeneous charge part of its name; the mixture is ignited without a spark plug, as in a diesel engine. In engineering jargon, this is a compression-ignition engine.
H.C.C.I. does not work at idle or near full throttle, so under these conditions the engine reverts to a conventional spark-ignition mode.
Every automaker is working on the H.C.C.I. combustion process, said Dr. Uwe Grebe, executive director for advanced engineering at General Motors Powertrain. Among the many attractions, he said, is that H.C.C.I. deals with mileage and emissions challenges inside the engine, rather than depending on devices like special catalytic converters to treat exhaust gas after it leaves the engine.
The high cylinder pressures of diesel engines, a result of compression ratios of 17 to 1 or more, raise the temperature high enough that ignition takes place spontaneously as fuel is injected into it. This fuel delivery into hot compressed air creates fuel-air mixtures all the way from 100 percent fuel to 100 percent air as fuel droplets evaporate and diffuse into the surrounding air. Upon igniting, combustion is hottest where fuel and air are ideally proportioned — hot enough to generate nitrogen oxides, the toughest exhaust emission to control.
As some larger fuel droplets fail to evaporate and do not burn completely, a carbon-rich residue is created. This is the source of diesel particulates — the black smoke once common from diesel exhaust pipes. If not for nitrogen oxides and particulates, the diesel engine’s high fuel efficiency would make it the most desirable automotive power plant.
In the type of gasoline spark-ignition engines that are dominant in the United States market, fuel and air are mixed before entering the engine cylinder. To cut emissions and increase fuel efficiency, it is desirable to burn lean mixtures in which there is less fuel in relation to the volume of air.
A lean mixture burns cooler than a chemically ideal mixture, and this lower temperature reduces formation of nitrogen oxides. The lower combustion temperature also makes the conversion of heat into pressure more efficient.
But lean mixtures are hard to ignite by spark, so engineers resort to stratifying the charge — injecting fuel in a layered pattern that is rich enough near the spark plug to ignite easily and leaving it leaner elsewhere. But the hot combustion of the fast-burning mixture near the spark plug again generates nitrogen oxides. If engineers try for higher fuel efficiency by raising the compression ratio to diesel-like numbers, the fuel knocks violently during combustion.
The germ of a compromise solution presented itself by accident. Have you ever had your car’s engine continue to run after its ignition was switched off? This “run-on,” as it is called, was especially common during the late 1970’s and ’80s. The engine runs roughly, bucks and finally stops — especially if you open the throttle.
Run-on is caused by chemical reactions in the fresh fuel-air mixture, driven by the heat of hot exhaust gas retained in the cylinder. Some have called run-on dieseling, but because it can occur at ordinary gasoline-engine compression ratios it is actually a different phenomenon.
This run-on process made engineers curious, and they have tested a number of engines based on the concept. The goal is to continuously proportion the fresh charge and the hot exhaust gas so that smooth auto-ignition is always achieved at the ideal time, as the piston nears the highest point of its travel in the cylinder.
Ignition in the H.C.C.I. operating mode takes place almost simultaneously at hundreds of points within the mixture, and the buildup of combustion pressure is smooth and fast. Compared with a well-designed conventional gasoline engine, H.C.C.I. offers the potential of a 30 percent improvement in fuel economy. Because its charge contains no hot-burning zones of mixture with chemically ideal proportions, H.C.C.I. can cut formation of nitrogen oxides to nearly zero.
These attractions are driving intensive H.C.C.I. development in many places, but the problems are daunting. First, at idle or low loads, too little exhaust heat is generated to maintain the self-ignition process, and above a 40 percent to 50 percent load, the cooling effect of so much fresh air-fuel mixture likewise puts out the fire. H.C.C.I. doesn’t work unless the engine is at least partly warmed up.
What can be done? One solution is to build a multimode engine that starts and operates on normal mixtures and spark ignition at very low loads, and then again from 40 percent to 100 percent load. In the middle, as cars cruised the freeways, drivers would enjoy great H.C.C.I. economy.
Honda built a demonstration two-stroke engine of this type in the 1990’s for an off-road racing motorcycle. Ben Knight, vice president for research and development of American Honda, said that the company had advanced beyond the test-bench stage with car engines, and is now working on a four-cylinder H.C.C.I. engine.
Any time a fresh concept appears, a wide range of possible uses arise. G.M. announced a joint development program with Stanford University and Bosch, the auto supplier, last year, and will have a “ready to drive” prototype on the road next year. “Gasoline engines could achieve 80 percent of diesel engine efficiency for about 50 percent of the cost,” said Dr. Gary Smyth, director of powertrain research at General Motors.
Promising technologies that shine in the controlled conditions of a research laboratory often fall short in the real world of stop-and-go commutes, freezing January mornings and traffic that hurtles along at extralegal freeway speeds. With H.C.C.I., the greatest challenge lies in smoothing the rough transitions between operating modes, something that human drivers are particularly sensitive to.
http://www.nytimes.com/2006/07/16/au...es/16BURN.html
July 16, 2006
Green Tech
A Well-Bred Engine Carries Best Genes of Its Parents
By KEVIN CAMERON
NO combustion process for converting fuel to forward motion is perfect. Though engineers can choose from a selection of combustion processes that have been developed for use in today’s automotive engines, each has some shortcoming — in efficiency, cost or environmental friendliness — that must be weighed against its benefits.
Gasoline engines, for instance, can be designed for very low exhaust emissions, but may leave something to be desired in efficiency. Small diesel engines can return terrific fuel economy, but they are costly, and scrubbing their exhaust gases to meet environmental regulations is a big challenge.
Often, the disadvantages that follow the “but” overwhelm the gains.
No wonder engineers are looking for new ways to combine the pluses of different engine types. One operating cycle for engines under wide study in the industry, known as Homogeneous Charge Compression Ignition, cherry-picks the best traits from gasoline and diesel designs — low emissions and high efficiency, respectively.
The H.C.C.I. engine runs ideally as a combination of the two. Like a spark-ignition engine, its fuel enters the cylinder premixed with air. The fuel is evenly distributed in the air — not concentrated around the fuel injection nozzle — accounting for the homogeneous charge part of its name; the mixture is ignited without a spark plug, as in a diesel engine. In engineering jargon, this is a compression-ignition engine.
H.C.C.I. does not work at idle or near full throttle, so under these conditions the engine reverts to a conventional spark-ignition mode.
Every automaker is working on the H.C.C.I. combustion process, said Dr. Uwe Grebe, executive director for advanced engineering at General Motors Powertrain. Among the many attractions, he said, is that H.C.C.I. deals with mileage and emissions challenges inside the engine, rather than depending on devices like special catalytic converters to treat exhaust gas after it leaves the engine.
The high cylinder pressures of diesel engines, a result of compression ratios of 17 to 1 or more, raise the temperature high enough that ignition takes place spontaneously as fuel is injected into it. This fuel delivery into hot compressed air creates fuel-air mixtures all the way from 100 percent fuel to 100 percent air as fuel droplets evaporate and diffuse into the surrounding air. Upon igniting, combustion is hottest where fuel and air are ideally proportioned — hot enough to generate nitrogen oxides, the toughest exhaust emission to control.
As some larger fuel droplets fail to evaporate and do not burn completely, a carbon-rich residue is created. This is the source of diesel particulates — the black smoke once common from diesel exhaust pipes. If not for nitrogen oxides and particulates, the diesel engine’s high fuel efficiency would make it the most desirable automotive power plant.
In the type of gasoline spark-ignition engines that are dominant in the United States market, fuel and air are mixed before entering the engine cylinder. To cut emissions and increase fuel efficiency, it is desirable to burn lean mixtures in which there is less fuel in relation to the volume of air.
A lean mixture burns cooler than a chemically ideal mixture, and this lower temperature reduces formation of nitrogen oxides. The lower combustion temperature also makes the conversion of heat into pressure more efficient.
But lean mixtures are hard to ignite by spark, so engineers resort to stratifying the charge — injecting fuel in a layered pattern that is rich enough near the spark plug to ignite easily and leaving it leaner elsewhere. But the hot combustion of the fast-burning mixture near the spark plug again generates nitrogen oxides. If engineers try for higher fuel efficiency by raising the compression ratio to diesel-like numbers, the fuel knocks violently during combustion.
The germ of a compromise solution presented itself by accident. Have you ever had your car’s engine continue to run after its ignition was switched off? This “run-on,” as it is called, was especially common during the late 1970’s and ’80s. The engine runs roughly, bucks and finally stops — especially if you open the throttle.
Run-on is caused by chemical reactions in the fresh fuel-air mixture, driven by the heat of hot exhaust gas retained in the cylinder. Some have called run-on dieseling, but because it can occur at ordinary gasoline-engine compression ratios it is actually a different phenomenon.
This run-on process made engineers curious, and they have tested a number of engines based on the concept. The goal is to continuously proportion the fresh charge and the hot exhaust gas so that smooth auto-ignition is always achieved at the ideal time, as the piston nears the highest point of its travel in the cylinder.
Ignition in the H.C.C.I. operating mode takes place almost simultaneously at hundreds of points within the mixture, and the buildup of combustion pressure is smooth and fast. Compared with a well-designed conventional gasoline engine, H.C.C.I. offers the potential of a 30 percent improvement in fuel economy. Because its charge contains no hot-burning zones of mixture with chemically ideal proportions, H.C.C.I. can cut formation of nitrogen oxides to nearly zero.
These attractions are driving intensive H.C.C.I. development in many places, but the problems are daunting. First, at idle or low loads, too little exhaust heat is generated to maintain the self-ignition process, and above a 40 percent to 50 percent load, the cooling effect of so much fresh air-fuel mixture likewise puts out the fire. H.C.C.I. doesn’t work unless the engine is at least partly warmed up.
What can be done? One solution is to build a multimode engine that starts and operates on normal mixtures and spark ignition at very low loads, and then again from 40 percent to 100 percent load. In the middle, as cars cruised the freeways, drivers would enjoy great H.C.C.I. economy.
Honda built a demonstration two-stroke engine of this type in the 1990’s for an off-road racing motorcycle. Ben Knight, vice president for research and development of American Honda, said that the company had advanced beyond the test-bench stage with car engines, and is now working on a four-cylinder H.C.C.I. engine.
Any time a fresh concept appears, a wide range of possible uses arise. G.M. announced a joint development program with Stanford University and Bosch, the auto supplier, last year, and will have a “ready to drive” prototype on the road next year. “Gasoline engines could achieve 80 percent of diesel engine efficiency for about 50 percent of the cost,” said Dr. Gary Smyth, director of powertrain research at General Motors.
Promising technologies that shine in the controlled conditions of a research laboratory often fall short in the real world of stop-and-go commutes, freezing January mornings and traffic that hurtles along at extralegal freeway speeds. With H.C.C.I., the greatest challenge lies in smoothing the rough transitions between operating modes, something that human drivers are particularly sensitive to.
http://www.nytimes.com/2006/07/16/au...es/16BURN.html
08-04-2006, 07:12 PM
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Sounds excessively complicated for new technology that was to have potential. Diesel will be accepted and will be the future here yet now we are to accept HCCI based off a turd of an article, cha right.
Last edited by heyitsme; 08-04-2006 at 07:14 PM.
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