Mkt intressant!
Detta är något alla bör känna till, till att börja med:
Citat:
Cold Starts
The high emissions regularly experienced during cold start are due primarily to
two reasons: low fuel volatility and poor catalytic converter performance. At 20 oC only
10-30% of gasoline actually vaporizes when injected into the combustion chamber. That
means 70-90% of the fuel remains in the liquid phase. Therefore the engine must inject
additional fuel to compensate for the low volatility. Typically this over compensation can
be from 8-15 times the stoichiometric amount in order to produce enough vapors for
reliable ignition. The non-vaporized fuel remains as a liquid till combustion. The fuel
vapors are ignited by the spark plug and most of the liquid fuel vaporizes and exits the
6
engine as unburned hydrocarbons. Overall this results in very rich air/fuel ratios that only
partially combust (Ashford, 2006).However, under ideal conditions the catalytic converter would eliminate many of
the unburned hydrocarbons by reduction and oxidation, but during this cold start period a
standard three-way convertor will not reach its “light off” (meaning a 50% hydrocarbon
conversion rate) temperature until 30-40 seconds after the start during the FTP drive
cycle. Unfortunately and ironically, the catalyst is the least efficient when it is most
needed during the operation of the vehicle. The result of this combination of less than
ideal circumstances is high tailpipe hydrocarbon emissions (Ashford, 2006)
Many researchers and inventors have focused on correcting these problems and
reducing hydrocarbon emissions during cold starts. Most of these projects have fallen
into two categories: improving engine starting parameters and improving catalytic
convertor performance. Recently there has been more work in a third category where
researchers use an alternative starting fuel in the engine during cold starts to reduce
emissions. While the other two categories attack the symptoms of the problem, this
approach actually deals with the low volatility of the fuel, the true cause of the problem
Bra sammanfattning kanske:
Citat:
Most recently at the University of Alabama, Ashford and Alff designed a bench
top Active Vapor Utilization System (AVUS). Unlike the work of Reddy and Servati,
AVUS actively collects vapor naturally produced in the fuel tank during normal operation
and diurnal temperature swings and returns the vapor to a liquid form for engine
operation. Liquid fuel solves a major problem of the Reddy and Servati systems,
unknown AFR. Once removed from the fuel tank, the vapors are compressed, cooled, and
stored in a pressurized tank for use in cold starting. Unfortunately, in Alff’s study the
AVUS condensate was unable to be tested in a vehicle and the industry standard ASTM
D86 Distillation test was unsuitable for testing due to the highly volatile nature of the
condensate. However, a simple evaporation test showed that the AVUS condensate
13
vaporizes at a rate nearly twice that of iso-pentane (Alff, 2007). The work presented here
looks to further investigate the practicality of the AVUS.
While these inventions have the potential to allow the gasoline engine to continue
to make cleaner power, many automobile makers are looking into alternative fuels as
ways to solve the emissions problems. Hydrogen, bio-diesel, electricity, and natural gas
are all possible energy sources for automobiles, but ethanol is one of the more plausible
and readily available alternatives that can be used today. In fact, thousands of vehicles
currently on the road are capable of functioning on ethanol mixtures as high as 85%
ethanol by volume. However, ethanol is much less volatile than commercial gasoline and
would lead to additional cold start problems. The use of AVUS on an E85 blend will also
be investigated.
Hmm, men i fig 6 ser man hur komlicerat detta blir..
Jag tror att vilken avancerad snabbvärmarlösning för etanolen vi än hittar på, så blir den enklare...
_________________
http://direktdemokraterna.seMyndigförklara dig själv.