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Homogenous Charge Combustion Ignition, or HCCI, is being developed by lots of organizations, because in theory, it has both better fuel economy and lower NOx emmisions.
In practice, however, there are problems.
If the engine uses minimal exhaust gas recirculation, then it needs very high compression
ratios -- similar to a diesel engine. An HCCI engine that uses these pressures produces the same kind of undesired noise that a diesel engines. Worse, when run under high load, the engine is prone to knocking.
An alternative way to design an HCCI engine (and the one recieving more development) is to work at lower pressures, similar to a conventional, spark-ignited, internal combustion engine. To achieve the necessary temperature for HCCI ignition, hot exhaust gas is recirculated. These engines too suffer problems -- most notably, during engine warm up, during idle, and under very low loads, the engine has trouble generating enough heat to produce a combustion ignition.
I propose a low pressure engine (i.e., similar pressures as a convetional spark ignition engine) which uses a mix of both liquid fuel, and boiled fuel.
The liquid fuel would be supplied in a conventional manner.
The fuel to be boiled would go from the fuel pump to a chamber in the engine, where the engine's heat would boil the fuel, and after boiling would be mixed with the air conventionally (either a venturi or an injector).
If the engine is cold, an electric heating element in the boiling chamber would provide the necessary heat.
As the engine warms up, or the load increases, the amount of boiled fuel is reduced or shut off entirely.
Boiled Gasoline Engine
Boiled_20Gasoline_20Engine
[phoenix, Apr 29 2009]
Heated intake air and fuel
Heated_20intake_20air_20and_20fuel
[phoenix, Apr 29 2009]
The heated, compressed fuel vapor system
The_20heated_2c_20c...el_20vapor_20system
[phoenix, Apr 29 2009]
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Annotation:
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In what way do you expect the boiled fuel to help?
The mass of fuel in the combustion chamber is very small compared to the mass of air (around 5%). Raising the temperature of 5% of the charge through 80°C or so will not make a significant difference to the heat of the total charge. What it will do is susbstantially increase the volume occupied by the boiled fuel and reduce the engine's volumetric effeciency. |
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whoa, don't get to technical here, [twiz] this isn't rocket science. You come here throwing around your two dollar words, I bet you don't even know what a word like "volumetric" even means. I'm sure that [bb] is on to something with this homogeneous/direct injection/otto cycle invention. (Although I'm pretty sure that a direct injection petrol engine utilizing a "hot bulb" combustion chamber is not "technically" a HCCI), it surely is another one of the secret technologies repressed by the oil companies. You work for the oil companies don't you [twiz] |
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I certainly don't work for any oil company. I work in motorsport (which may be 'just as bad' from your viewpoint).
By 'volumetric effeciency' (a £1 phrase) I am referring to the volume of charge which the engine can draw into its combustion chamber relative to the swept volume of the cylinder. |
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Among the better known mechanisms for improving volumetric effeciency is the intercooler, which reduces the temperature of the charge before it enters the combustion chamber. |
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If you want to add heat to the charge, the time to do it is after the valves have closed! |
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I'm sure the oil companies would promote anything which makes oil consuming engines look better, rather than see them overtaken by alternative fuel sources. |
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simmer down sport I was just kidding. I too am involved in motorsport here in the US. Many HB ideas about engines are ludicrous hodgepodges of technical words and poorly misunderstood design concepts. If the idea didn't make much sense in the first place then it isn't likely that the author will see the flaw when you explain it. Furthermore since the ICE is easy to speculate about but hard to prototype, many ideas don't die simply because nobody has the desire to debunk them. |
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When a mixture of droplets of liquid fuel and air is compressed, the temperature rises more slowly than it would if one were compressing air alone in the same manner, since the liquid absorbs heat (its heat of fusion) and evaporates/boils. |
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The purpose of using preboiled fuel isn't to increase the amount of starting heat; it's to reduce or eliminate the heat-absorbing capacity of the fuel. |
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And as for loss of efficiency -- I only expect the engine to use boiled fuel when it is cold, idle, or under low load. |
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see, the really big problem is getting people to understand that the thermodynamics of the mixture before combustion actually need to be pretty "cold" and somewhat below the autoignition threshold to allow a uniform burn. I see no application for a hot bulb combustion chamber in a modern high efficiency, high output/lb, engine and I suspect that they are a bit of an emissions nightmare. Actually this sounds more like an Idea for Ye Olde Half-Biscuit a single sheet circular for the dissemination of new untested ideas printed circa 1900. |
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WcW, has anyone told you that your annotations are amazing? |
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So amazing, in fact, that I can't understand what it is you're talking about. |
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Sure, I understand that under normal operation, the air needs to be cold before compression, otherwise we end up with a reduced mass of air in the piston, which in turn reduces power. Do we need very high power during the first few seconds when the engine is starting up? Do we need very high power when the engine is idling? Do we need very high power when the engine is under low load? |
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Furthermore, in a spark-ignited engine, I understand why a slow burn is desireable. |
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Why do you believe that a slow burn is also desirable (or even possible) in a compression ignited engine? |
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As for a hot bulb combustion chamber.. wtf are you talking about? |
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