12.3:1 CR? Runnable on pump gas?
03-Apr-2003, 09:07 AM
#7
Registered User
Join Date: Apr 2002
Posts: 443
I'm running over 13:1 compression on 94 octane no problem. just had to retard the timing slightly. I wish that I had gone with higher compression. I've seen as high as 14:1 compression on 94 octane. this was on a honda of course. for some reason, hondas like running a little lean. if you try to run 12:1 compression on, let's say a neon, you'd blow that bitch in no time.
04-Apr-2003, 01:59 PM
#15
Registered User
Thread Starter
Join Date: Apr 2002
Posts: 3,084
Originally posted by b16civic
do you guys acctully know the compression you are running? or are you guessing? i have seen guys throw ctr pistons in an engine which should bring you up to about 12:1 and the wind up with holes in the top of their pistons. there are reasons that you dont get high compression engines in Canada. we dont have 102 octaine like japan at the pumps. but what do i know.
do you guys acctully know the compression you are running? or are you guessing? i have seen guys throw ctr pistons in an engine which should bring you up to about 12:1 and the wind up with holes in the top of their pistons. there are reasons that you dont get high compression engines in Canada. we dont have 102 octaine like japan at the pumps. but what do i know.
I'd just like to get more opinions and experiences
Out of the situations you have seen people putting in CTR slugs in and them blowing holes in the top, what was the condition for them blowing a hole in it? Just normal driving? I'd like to hear more about this
thanks
05-Apr-2003, 10:13 AM
#16
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Join Date: Apr 2002
Location: HOCKEY CAPITAL OF THE WORLD
Posts: 1,075
Originally posted by b16civic
im not offended...geez im not a child. guys what im saying is that 12.5:1 is too high for 94 octaine. for example NASCAR engines run at 14:1 on 112 octaine or 110 but its up there. they are not using 102 cause they will blow sky high. just do the math. thats all im saying. we build engines for a LIVING. its our job to know this. endyne has pistons they say are 12:1 for pump gas but they are special design "roller wave" or something like that. if they have a special design to run that compresion and the ctr doesnt what does that tell you?
im not offended...geez im not a child. guys what im saying is that 12.5:1 is too high for 94 octaine. for example NASCAR engines run at 14:1 on 112 octaine or 110 but its up there. they are not using 102 cause they will blow sky high. just do the math. thats all im saying. we build engines for a LIVING. its our job to know this. endyne has pistons they say are 12:1 for pump gas but they are special design "roller wave" or something like that. if they have a special design to run that compresion and the ctr doesnt what does that tell you?
05-Apr-2003, 08:21 PM
#17
Guest
Join Date: Sep 2002
Posts: 957
Do what ever your want ryuujin, I personally think you should do it. The computer will adjust some what, modern engine have computers that will adjust to temps, humid., pressure etc...
From http://www.seansa4page.com/resource/octane.html
Look around on this site there is a guide to compression.
Subject: 7. What parameters determine octane requirement?
7.1 What is the effect of Compression ratio?
Most people know that an increase in Compression Ratio will require an
increase in fuel octane for the same engine design. Increasing the
compression ratio increases the theoretical thermodynamic efficiency of an
engine according to the standard equation
Efficiency = 1 - (1/compression ratio)^gamma-1
where gamma = ratio of specific heats at constant pressure and constant
volume of the working fluid ( for most purposes air is the working fluid,
and is treated as an ideal gas ). There are indications that thermal
efficiency reaches a maximum at a compression ratio of about 17:1 [15].
The efficiency gains are best when the engine is at incipient knock, that's why knock sensors ( actually vibration sensors ) are used. Low compression ratio engines are less efficient because they can not deliver as much of the ideal combustion power to the flywheel. For a typical carburetted engine, without engine management [17,24]:-
Compression Octane Number Brake Thermal Efficiency
Ratio Requirement ( Full Throttle )
5:1 72 -
6:1 81 25 %
7:1 87 28 %
8:1 92 32 %
9:1 96 32 %
10:1 100 33 %
11:1 104 34 %
12:1 108 35 %
Modern engines have improved significantly on this, and the changing fuel
specifications and engine design should see more improvements, but
significant gains may have to await improved engine materials and fuels.
7.2 What is the effect of changing the air/fuel ratio?
Traditionally, the greatest tendency to knock was near 13.5:1 air/fuel
ratio, but was very engine specific. Modern engines, with engine management
systems, now have their maximum octane requirement near to 14.5:1. For a
given engine using gasoline, the relationship between thermal efficiency,
air/fuel ratio, and power is complex. Stoichiometric combustion ( Air/Fuel
Ratio = 14.7:1 for a typical non-oxygenated gasoline ) is neither maximum
power - which occurs around A/F 12-13:1 (Rich), nor maximum thermal
efficiency - which occurs around A/F 16-18:1 (Lean). The air-fuel ratio is
controlled at part throttle by a closed loop system using the oxygen sensor
in the exhaust. Conventionally, enrichment for maximum power air/fuel ratio
is used during full throttle operation to reduce knocking while providing
better driveability [24]. If the mixture is weakened, the flame speed is
reduced, consequently less heat is converted to mechanical energy, leaving
heat in the cylinder walls and head, potentially inducing knock. It is
possible to weaken the mixture sufficiently that the flame is still present
when the inlet valve opens again, resulting in backfiring.
7.3 What is the effect of changing the ignition timing
The tendency to knock increases as spark advance is increased, eg 2 degrees
BTDC requires 91 octane, whereas 14 degrees BTDC requires 96 octane.
If you advance the spark, the flame front starts earlier, and the end gases
start forming earlier in the cycle, providing more time for the autoigniting
species to form before the piston reaches the optimum position for power
delivery, as determined by the normal flame front propagation. It becomes a
race between the flame front and decomposition of the increasingly-squashed
end gases. High octane fuels produce end gases that take longer to
autoignite, so the good flame front reaches and consumes them properly.
The ignition advance map is partly determined by the fuel the engine is intended to use. The timing of the spark is advanced sufficiently to ensure that the fuel/air mixture burns in such a way that maximum pressure of the burning charge is about 15-20 degree after TDC. Knock will occur before this point, usually in the late compression/early power stroke period. The engine management system uses ignition timing as one of the major variables that is adjusted if knock is detected. If very low octane fuels are used ( several octane numbers below the vehicle's requirement at optimal settings ), both performance and fuel economy will decrease.
The actual Octane Number Requirement depends on the engine design, but for some 1978 vehicles using standard fuels, the following (R+M)/2 Octane Requirements were measured. "Standard" is the recommended ignition timing for the engine, probably a few degrees before Top Dead Centre [24].
Basic Ignition Timing
Vehicle Retarded 5 degrees Standard Advanced 5 degrees
A 88 91 93
B 86 90.5 94.5
C 85.5 88 90
D 84 87.5 91
E 82.5 87 90
The actual ignition timing to achieve the maximum pressure from normal
combustion of gasoline will depend mainly on the speed of the engine and the
flame propagation rates in the engine. Knock increases the rate of the
pressure rise, thus superimposing additional pressure on the normal
combustion pressure rise. The knock actually rapidly resonates around the
chamber, creating a series of abnormal sharp spikes on the pressure diagram.
The normal flame speed is fairly consistent for most gasoline HCs, regardless
of octane rating, but the flame speed is affected by stoichiometry. Note that
the flame speeds in this FAQ are not the actual engine flame speeds. A 12:1
CR gasoline engine at 1500 rpm would have a flame speed of about 16.5 m/s,
and a similar hydrogen engine yields 48.3 m/s, but such engine flame speeds
are also very dependent on stoichiometry.
7.4 What is the effect of engine management systems?
Engine management systems are now an important part of the strategy to
reduce automotive pollution. The good news for the consumer is their ability
to maintain the efficiency of gasoline combustion, thus improving fuel
economy. The bad news is their tendency to hinder tuning for power. A very
basic modern engine system could monitor and control:- mass air flow, fuel
flow, ignition timing, exhaust oxygen ( lambda oxygen sensor ), knock
( vibration sensor ), EGR, exhaust gas temperature, coolant temperature, and
intake air temperature. The knock sensor can be either a nonresonant type
installed in the engine block and capable of measuring a wide range of knock
vibrations ( 5-15 kHz ) with minimal change in frequency, or a resonant type
that has excellent signal-to-noise ratio between 1000 and 5000 rpm [72].
A modern engine management system can compensate for altitude, ambient air temperature, and fuel octane. The management system will also control cold start settings, and other operational parameters. There is a new requirement that the engine management system also contain an on-board diagnostic function that warns of malfunctions such as engine misfire, exhaust catalyst failure, and evaporative emissions failure. The use of fuels with alcohols such as methanol can confuse the engine management system as they generate more hydrogen which can fool the oxygen sensor [47] .
The use of fuel of too low octane can actually result in both a loss of fuel economy and power, as the management system may have to move the engine settings to a less efficient part of the performance map. The system retards the ignition timing until only trace knock is detected, as engine damage from knock is of more consequence than power and fuel economy.
7.5 What is the effect of temperature and load?
Increasing the engine temperature, particularly the air/fuel charge
temperature, increases the tendency to knock. The Sensitivity of a fuel can
indicate how it is affected by charge temperature variations. Increasing
load increases both the engine temperature, and the end-gas pressure, thus
the likelihood of knock increases as load increases.
7.6 What is the effect of engine speed?
Faster engine speed means there is less time for the pre-flame reactions
in the end gases to occur, thus reducing the tendency to knock. On engines
with management systems, the ignition timing may be advanced with engine
speed and load, to obtain optimum efficiency at incipient knock. In such
cases, both high and low engines speeds may be critical.
7.7 What is the effect of engine deposits?
A new engine may only require a fuel of 6-9 octane numbers lower than the
same engine after 25,000 km. This Octane Requirement Increase (ORI) is due to
the formation of a mixture of organic and inorganic deposits resulting from
both the fuel and the lubricant. They reach an equilibrium amount because
of flaking, however dramatic changes in driving styles can also result in
dramatic changes of the equilibrium position. When the engine starts to burn
more oil, the octane requirement can increase again. ORIs up to 12 are not
uncommon, depending on driving style [17,19]. The deposits produce the ORI
by several mechanisms:-
- they reduce the combustion chamber volume, effectively increasing the compression ratio. - they also reduce thermal conductivity, thus increasing the combustion chamber temperatures. - they catalyse undesirable pre-flame reactions that produce end gases with low autoignition temperatures.
7.8 What is the Road Octane requirement of an vehicle?
The actual octane requirements of a vehicle is called the Octane Number
Requirement ( ONR ), and is determined by using standard octane fuels that
can be blends of iso-octane and normal heptane, or commercial gasolines.
The vehicle is tested under a wide range of conditions and loads, using
different octane fuels until trace knock is detected. The conditions that
require maximum octane are not consistent, but often are full-throttle
acceleration from low starting speeds using the highest gear available. They
can even be at constant speed conditions [17]. Engine management systems
that adjust the octane requirement may also reduce the power output on low
octane fuel, resulting in increased fuel consumption. The maximum ONR is of
most interest, as that usually defines the recommended fuel.
The octane rating engines do not reflect actual conditions in a vehicle, consequently there are standard procedures for evaluating the performance of the gasoline in an engine. The most common are:- 1. The Modified Uniontown Procedure. Full throttle accelerations are made from low speed using primary reference fuels. The ignition timing is adjusted until trace knock is detected at some stage. Several reference fuels are used, and a Road Octane Number v Basic Ignition timing graph is obtained. The fuel sample is tested, and the ignition timing setting is read from the graph to provide the Road Octane Number. This is a rapid procedure but provides minimal information. 2. The Modified Borderline Knock Procedure. The automatic spark advance is disabled, and a manual adjustment facility added. Accelerations are performed as in the Modified Uniontown Procedure, however trace knock is maintained throughout the run. A map of ignition advance v engine speed is made for several reference fuels and the sample fuels. This procedure can show the variation of road octane with engine speed.
7.9 What is the effect of air temperature?
An increase in ambient air temperature of 5.6C increases the octane
requirement of an engine by 0.44 - 0.54 MON [17,24]. When the combined effects
of air temperature and humidity are considered, it is often possible to use
one octane grade in summer, and use a lower octane rating in winter. The
Motor octane rating has a higher charge temperature, and increasing charge
temperature increases the tendency to knock, so fuels with low Sensitivity
( the difference between RON and MON numbers ) are less affected by air
temperature.
7.10 What is the effect of altitude?
The effect of increasing altitude may be nonlinear, with one study reporting
a decrease of the octane requirement of 1.4 RON/300m from sea level to 1800m
and 2.5 RON/300m from 1800m to 3600m [17]. Other studies report the octane
number requirement decreased by 1.0 - 1.9 RON/300m without specifying
altitude [24]. Modern engine management systems can accommodate this
adjustment, and in some recent studies, the octane number requirement was
0.2 - 0.5 Antiknock Index/300m. The reduction on older engines was due to:-
- reduced air density provides lower combustion temperature and pressure. - fuel is metered according to air volume, consequently as density decreases the stoichiometry moves to rich, with a lower octane number requirement. - manifold vacuum controlled spark advance, and reduced manifold vacuum results in less spark advance.
7.11 What is the effect of humidity?
An increase of absolute humidity of 1.0 g water/ kg of dry air lowers the
octane requirement of an engine by 0.25 - 0.32 MON [17,24].
7.12 What does water injection achieve?
Water injection was used in WWII aviation engine to provide a large increase
in available power for very short periods. The injection of water does
decrease the dew point of the exhaust gases. This has potential corrosion
problems. The very high specific heat and heat of vaporisation of water
means that the combustion temperature will decrease. It has been shown that
a 10% water addition to methanol reduces the power and efficiency by about
3%, and doubles the unburnt fuel emissions, but does reduce NOx by 25% [73].
A decrease in combustion temperature will reduce the theoretical maximum
possible efficiency of an otto cycle engine that is operating correctly,
but may improve efficiency in engines that are experiencing abnormal
combustion on existing fuels.
Some aviation SI engines still use boost fluids. The water/methanol mixtures are used to provide increased power for short periods, up to 40% more - assuming adequate mechanical strength of the engine. The 40/60 or 45/55 water/methanol mixtures are used as boost fluids for aviation engines because water would freeze. Methanol is just "preburnt" methane, consequently it only has about half the energy content of gasoline, but it does have a higher heat of vaporisation, which has a significant cooling effect on the charge. Water/methanol blends are more cost-effective than gasoline for combustion cooling. The high Sensitivity of alcohol fuels has to be considered in the engine design and settings.
Boost fluids are used because they are far more economical than using the fuel. When a supercharged engine has to be operated at high boost, the mixture has to be enriched to keep the engine operating without knock. The extra fuel cools the cylinder walls and the charge, thus delaying the onset of knock which would otherwise occur at the associated higher temperatures.
The overall effect of boost fluid injection is to permit a considerable increase in knock-free engine power for the same combustion chamber temperature. The power increase is obtained from the higher allowable boost. In practice, the fuel mixture is usually weakened when using boost fluid injection, and the ratio of the two fuel fluids is approximately 100 parts of avgas to 25 parts of boost fluid. With that ratio, the resulting performance corresponds to an effective uprating of the fuel of about 25%, irrespective of its original value. Trying to increase power boosting above 40% is difficult, as the engine can drown because of excessive liquid [71].
Note that for water injection to provide useful power gains, the engine management and fuel systems must be able to monitor the knock and adjust both stoichiometry and ignition to obtain significant benefits. Aviation engines are designed to accommodate water injection, most automobile engines are not. Returns on investment are usually harder to achieve on engines that do not normal extend their performance envelope into those regions. Water injection has been used by some engine manufacturers - usually as an expedient way to maintain acceptable power after regulatory emissions baggage was added to the engine, but usually the manufacturer quickly produces a modified engine that does not require water injection.
From http://www.seansa4page.com/resource/octane.html
Look around on this site there is a guide to compression.
Subject: 7. What parameters determine octane requirement?
7.1 What is the effect of Compression ratio?
Most people know that an increase in Compression Ratio will require an
increase in fuel octane for the same engine design. Increasing the
compression ratio increases the theoretical thermodynamic efficiency of an
engine according to the standard equation
Efficiency = 1 - (1/compression ratio)^gamma-1
where gamma = ratio of specific heats at constant pressure and constant
volume of the working fluid ( for most purposes air is the working fluid,
and is treated as an ideal gas ). There are indications that thermal
efficiency reaches a maximum at a compression ratio of about 17:1 [15].
The efficiency gains are best when the engine is at incipient knock, that's why knock sensors ( actually vibration sensors ) are used. Low compression ratio engines are less efficient because they can not deliver as much of the ideal combustion power to the flywheel. For a typical carburetted engine, without engine management [17,24]:-
Compression Octane Number Brake Thermal Efficiency
Ratio Requirement ( Full Throttle )
5:1 72 -
6:1 81 25 %
7:1 87 28 %
8:1 92 32 %
9:1 96 32 %
10:1 100 33 %
11:1 104 34 %
12:1 108 35 %
Modern engines have improved significantly on this, and the changing fuel
specifications and engine design should see more improvements, but
significant gains may have to await improved engine materials and fuels.
7.2 What is the effect of changing the air/fuel ratio?
Traditionally, the greatest tendency to knock was near 13.5:1 air/fuel
ratio, but was very engine specific. Modern engines, with engine management
systems, now have their maximum octane requirement near to 14.5:1. For a
given engine using gasoline, the relationship between thermal efficiency,
air/fuel ratio, and power is complex. Stoichiometric combustion ( Air/Fuel
Ratio = 14.7:1 for a typical non-oxygenated gasoline ) is neither maximum
power - which occurs around A/F 12-13:1 (Rich), nor maximum thermal
efficiency - which occurs around A/F 16-18:1 (Lean). The air-fuel ratio is
controlled at part throttle by a closed loop system using the oxygen sensor
in the exhaust. Conventionally, enrichment for maximum power air/fuel ratio
is used during full throttle operation to reduce knocking while providing
better driveability [24]. If the mixture is weakened, the flame speed is
reduced, consequently less heat is converted to mechanical energy, leaving
heat in the cylinder walls and head, potentially inducing knock. It is
possible to weaken the mixture sufficiently that the flame is still present
when the inlet valve opens again, resulting in backfiring.
7.3 What is the effect of changing the ignition timing
The tendency to knock increases as spark advance is increased, eg 2 degrees
BTDC requires 91 octane, whereas 14 degrees BTDC requires 96 octane.
If you advance the spark, the flame front starts earlier, and the end gases
start forming earlier in the cycle, providing more time for the autoigniting
species to form before the piston reaches the optimum position for power
delivery, as determined by the normal flame front propagation. It becomes a
race between the flame front and decomposition of the increasingly-squashed
end gases. High octane fuels produce end gases that take longer to
autoignite, so the good flame front reaches and consumes them properly.
The ignition advance map is partly determined by the fuel the engine is intended to use. The timing of the spark is advanced sufficiently to ensure that the fuel/air mixture burns in such a way that maximum pressure of the burning charge is about 15-20 degree after TDC. Knock will occur before this point, usually in the late compression/early power stroke period. The engine management system uses ignition timing as one of the major variables that is adjusted if knock is detected. If very low octane fuels are used ( several octane numbers below the vehicle's requirement at optimal settings ), both performance and fuel economy will decrease.
The actual Octane Number Requirement depends on the engine design, but for some 1978 vehicles using standard fuels, the following (R+M)/2 Octane Requirements were measured. "Standard" is the recommended ignition timing for the engine, probably a few degrees before Top Dead Centre [24].
Basic Ignition Timing
Vehicle Retarded 5 degrees Standard Advanced 5 degrees
A 88 91 93
B 86 90.5 94.5
C 85.5 88 90
D 84 87.5 91
E 82.5 87 90
The actual ignition timing to achieve the maximum pressure from normal
combustion of gasoline will depend mainly on the speed of the engine and the
flame propagation rates in the engine. Knock increases the rate of the
pressure rise, thus superimposing additional pressure on the normal
combustion pressure rise. The knock actually rapidly resonates around the
chamber, creating a series of abnormal sharp spikes on the pressure diagram.
The normal flame speed is fairly consistent for most gasoline HCs, regardless
of octane rating, but the flame speed is affected by stoichiometry. Note that
the flame speeds in this FAQ are not the actual engine flame speeds. A 12:1
CR gasoline engine at 1500 rpm would have a flame speed of about 16.5 m/s,
and a similar hydrogen engine yields 48.3 m/s, but such engine flame speeds
are also very dependent on stoichiometry.
7.4 What is the effect of engine management systems?
Engine management systems are now an important part of the strategy to
reduce automotive pollution. The good news for the consumer is their ability
to maintain the efficiency of gasoline combustion, thus improving fuel
economy. The bad news is their tendency to hinder tuning for power. A very
basic modern engine system could monitor and control:- mass air flow, fuel
flow, ignition timing, exhaust oxygen ( lambda oxygen sensor ), knock
( vibration sensor ), EGR, exhaust gas temperature, coolant temperature, and
intake air temperature. The knock sensor can be either a nonresonant type
installed in the engine block and capable of measuring a wide range of knock
vibrations ( 5-15 kHz ) with minimal change in frequency, or a resonant type
that has excellent signal-to-noise ratio between 1000 and 5000 rpm [72].
A modern engine management system can compensate for altitude, ambient air temperature, and fuel octane. The management system will also control cold start settings, and other operational parameters. There is a new requirement that the engine management system also contain an on-board diagnostic function that warns of malfunctions such as engine misfire, exhaust catalyst failure, and evaporative emissions failure. The use of fuels with alcohols such as methanol can confuse the engine management system as they generate more hydrogen which can fool the oxygen sensor [47] .
The use of fuel of too low octane can actually result in both a loss of fuel economy and power, as the management system may have to move the engine settings to a less efficient part of the performance map. The system retards the ignition timing until only trace knock is detected, as engine damage from knock is of more consequence than power and fuel economy.
7.5 What is the effect of temperature and load?
Increasing the engine temperature, particularly the air/fuel charge
temperature, increases the tendency to knock. The Sensitivity of a fuel can
indicate how it is affected by charge temperature variations. Increasing
load increases both the engine temperature, and the end-gas pressure, thus
the likelihood of knock increases as load increases.
7.6 What is the effect of engine speed?
Faster engine speed means there is less time for the pre-flame reactions
in the end gases to occur, thus reducing the tendency to knock. On engines
with management systems, the ignition timing may be advanced with engine
speed and load, to obtain optimum efficiency at incipient knock. In such
cases, both high and low engines speeds may be critical.
7.7 What is the effect of engine deposits?
A new engine may only require a fuel of 6-9 octane numbers lower than the
same engine after 25,000 km. This Octane Requirement Increase (ORI) is due to
the formation of a mixture of organic and inorganic deposits resulting from
both the fuel and the lubricant. They reach an equilibrium amount because
of flaking, however dramatic changes in driving styles can also result in
dramatic changes of the equilibrium position. When the engine starts to burn
more oil, the octane requirement can increase again. ORIs up to 12 are not
uncommon, depending on driving style [17,19]. The deposits produce the ORI
by several mechanisms:-
- they reduce the combustion chamber volume, effectively increasing the compression ratio. - they also reduce thermal conductivity, thus increasing the combustion chamber temperatures. - they catalyse undesirable pre-flame reactions that produce end gases with low autoignition temperatures.
7.8 What is the Road Octane requirement of an vehicle?
The actual octane requirements of a vehicle is called the Octane Number
Requirement ( ONR ), and is determined by using standard octane fuels that
can be blends of iso-octane and normal heptane, or commercial gasolines.
The vehicle is tested under a wide range of conditions and loads, using
different octane fuels until trace knock is detected. The conditions that
require maximum octane are not consistent, but often are full-throttle
acceleration from low starting speeds using the highest gear available. They
can even be at constant speed conditions [17]. Engine management systems
that adjust the octane requirement may also reduce the power output on low
octane fuel, resulting in increased fuel consumption. The maximum ONR is of
most interest, as that usually defines the recommended fuel.
The octane rating engines do not reflect actual conditions in a vehicle, consequently there are standard procedures for evaluating the performance of the gasoline in an engine. The most common are:- 1. The Modified Uniontown Procedure. Full throttle accelerations are made from low speed using primary reference fuels. The ignition timing is adjusted until trace knock is detected at some stage. Several reference fuels are used, and a Road Octane Number v Basic Ignition timing graph is obtained. The fuel sample is tested, and the ignition timing setting is read from the graph to provide the Road Octane Number. This is a rapid procedure but provides minimal information. 2. The Modified Borderline Knock Procedure. The automatic spark advance is disabled, and a manual adjustment facility added. Accelerations are performed as in the Modified Uniontown Procedure, however trace knock is maintained throughout the run. A map of ignition advance v engine speed is made for several reference fuels and the sample fuels. This procedure can show the variation of road octane with engine speed.
7.9 What is the effect of air temperature?
An increase in ambient air temperature of 5.6C increases the octane
requirement of an engine by 0.44 - 0.54 MON [17,24]. When the combined effects
of air temperature and humidity are considered, it is often possible to use
one octane grade in summer, and use a lower octane rating in winter. The
Motor octane rating has a higher charge temperature, and increasing charge
temperature increases the tendency to knock, so fuels with low Sensitivity
( the difference between RON and MON numbers ) are less affected by air
temperature.
7.10 What is the effect of altitude?
The effect of increasing altitude may be nonlinear, with one study reporting
a decrease of the octane requirement of 1.4 RON/300m from sea level to 1800m
and 2.5 RON/300m from 1800m to 3600m [17]. Other studies report the octane
number requirement decreased by 1.0 - 1.9 RON/300m without specifying
altitude [24]. Modern engine management systems can accommodate this
adjustment, and in some recent studies, the octane number requirement was
0.2 - 0.5 Antiknock Index/300m. The reduction on older engines was due to:-
- reduced air density provides lower combustion temperature and pressure. - fuel is metered according to air volume, consequently as density decreases the stoichiometry moves to rich, with a lower octane number requirement. - manifold vacuum controlled spark advance, and reduced manifold vacuum results in less spark advance.
7.11 What is the effect of humidity?
An increase of absolute humidity of 1.0 g water/ kg of dry air lowers the
octane requirement of an engine by 0.25 - 0.32 MON [17,24].
7.12 What does water injection achieve?
Water injection was used in WWII aviation engine to provide a large increase
in available power for very short periods. The injection of water does
decrease the dew point of the exhaust gases. This has potential corrosion
problems. The very high specific heat and heat of vaporisation of water
means that the combustion temperature will decrease. It has been shown that
a 10% water addition to methanol reduces the power and efficiency by about
3%, and doubles the unburnt fuel emissions, but does reduce NOx by 25% [73].
A decrease in combustion temperature will reduce the theoretical maximum
possible efficiency of an otto cycle engine that is operating correctly,
but may improve efficiency in engines that are experiencing abnormal
combustion on existing fuels.
Some aviation SI engines still use boost fluids. The water/methanol mixtures are used to provide increased power for short periods, up to 40% more - assuming adequate mechanical strength of the engine. The 40/60 or 45/55 water/methanol mixtures are used as boost fluids for aviation engines because water would freeze. Methanol is just "preburnt" methane, consequently it only has about half the energy content of gasoline, but it does have a higher heat of vaporisation, which has a significant cooling effect on the charge. Water/methanol blends are more cost-effective than gasoline for combustion cooling. The high Sensitivity of alcohol fuels has to be considered in the engine design and settings.
Boost fluids are used because they are far more economical than using the fuel. When a supercharged engine has to be operated at high boost, the mixture has to be enriched to keep the engine operating without knock. The extra fuel cools the cylinder walls and the charge, thus delaying the onset of knock which would otherwise occur at the associated higher temperatures.
The overall effect of boost fluid injection is to permit a considerable increase in knock-free engine power for the same combustion chamber temperature. The power increase is obtained from the higher allowable boost. In practice, the fuel mixture is usually weakened when using boost fluid injection, and the ratio of the two fuel fluids is approximately 100 parts of avgas to 25 parts of boost fluid. With that ratio, the resulting performance corresponds to an effective uprating of the fuel of about 25%, irrespective of its original value. Trying to increase power boosting above 40% is difficult, as the engine can drown because of excessive liquid [71].
Note that for water injection to provide useful power gains, the engine management and fuel systems must be able to monitor the knock and adjust both stoichiometry and ignition to obtain significant benefits. Aviation engines are designed to accommodate water injection, most automobile engines are not. Returns on investment are usually harder to achieve on engines that do not normal extend their performance envelope into those regions. Water injection has been used by some engine manufacturers - usually as an expedient way to maintain acceptable power after regulatory emissions baggage was added to the engine, but usually the manufacturer quickly produces a modified engine that does not require water injection.
05-Apr-2003, 08:26 PM
#18
Guest
Join Date: Sep 2002
Posts: 957
Here you go.
http://www.nsxprime.com/FAQ/Miscellaneous/FuelAdditives.htm
I got the following from the above
GT-100 Unleaded, is a clear fuel with a pump octane of 100, and will handle compression ratios of up to 12:1, and is street legal in all 50 states.
GT PLUS, is also unleaded, and is rated at 104 octane. It is suitable for compression ratios up to 14:1 and is colored light blue. It will not harm oxygen sensors or knock sensors in computer controlled engines. It is not street legal.
STANDARD, is a leaded fuel rated at 110 octane, is colored purple, and is intended for drag racing, road racing, and race boats.
SUPREME, is also a leaded fuel and is dark blue. It was developed to help resist vapor lock and meet the demands of sportsman, modifieds, offshore powerboats, and endurance racing where engines regularly run in excess of 7000 rpm.
MAXIMAL, we mentioned earlier, is colored red, has 116 octane, and is leaded. It is intended for exceptionally high performance applications like Pro Stock where extremely high cylinder pressures are common. Its extremely fast burn rate is satisfactory where rpm exceeds 10,000.
Now that you're an expert on gasolines, you probably would like to know where to buy and store the stuff. If you are fortunate enough to live in the mid-Atlantic states, you can take advantage of Sunoco's GT-100 Unleaded retail pilot program and get 100 octane race fuel at pumps located at select Sunoco stations. The rest of us have to purchase from local speed shops, at race tracks, or directly from Sunoco distributors.
When you plan on buying fuel in quantity, say a 55-gallon drum, you'll be happy to know that racing fuel has a shelf life of about a year, if you store it properly. The container must conform to all safety standards, and should be made from metal or polymer. Make sure the container is opaque and solid in color. The white plastic jugs we see at the track should be used for short-term storage only. They let in sunlight, which will affect the fuel. The lead in leaded fuel and other chemicals in unleaded fuel are photosensitive, and will dissipate if they am exposed to the sun. Keep any container tightly sealed to prevent evaporation.
http://www.nsxprime.com/FAQ/Miscellaneous/FuelAdditives.htm
I got the following from the above
GT-100 Unleaded, is a clear fuel with a pump octane of 100, and will handle compression ratios of up to 12:1, and is street legal in all 50 states.
GT PLUS, is also unleaded, and is rated at 104 octane. It is suitable for compression ratios up to 14:1 and is colored light blue. It will not harm oxygen sensors or knock sensors in computer controlled engines. It is not street legal.
STANDARD, is a leaded fuel rated at 110 octane, is colored purple, and is intended for drag racing, road racing, and race boats.
SUPREME, is also a leaded fuel and is dark blue. It was developed to help resist vapor lock and meet the demands of sportsman, modifieds, offshore powerboats, and endurance racing where engines regularly run in excess of 7000 rpm.
MAXIMAL, we mentioned earlier, is colored red, has 116 octane, and is leaded. It is intended for exceptionally high performance applications like Pro Stock where extremely high cylinder pressures are common. Its extremely fast burn rate is satisfactory where rpm exceeds 10,000.
Now that you're an expert on gasolines, you probably would like to know where to buy and store the stuff. If you are fortunate enough to live in the mid-Atlantic states, you can take advantage of Sunoco's GT-100 Unleaded retail pilot program and get 100 octane race fuel at pumps located at select Sunoco stations. The rest of us have to purchase from local speed shops, at race tracks, or directly from Sunoco distributors.
When you plan on buying fuel in quantity, say a 55-gallon drum, you'll be happy to know that racing fuel has a shelf life of about a year, if you store it properly. The container must conform to all safety standards, and should be made from metal or polymer. Make sure the container is opaque and solid in color. The white plastic jugs we see at the track should be used for short-term storage only. They let in sunlight, which will affect the fuel. The lead in leaded fuel and other chemicals in unleaded fuel are photosensitive, and will dissipate if they am exposed to the sun. Keep any container tightly sealed to prevent evaporation.
15-Apr-2003, 10:57 AM
#19
Registered User
Join Date: Apr 2002
Posts: 443
Originally posted by b16civic
i was told today by someone that knows you that you run octaine booster. is this true? also i was told that you broke the engine in on 112. why would that be?
i was told today by someone that knows you that you run octaine booster. is this true? also i was told that you broke the engine in on 112. why would that be?
who would that someone be? just curious...
yes, I broke the engine in on C12 (112 octane) because I was worried about detonation from running 12.5:1+ compression. after the break in I ran 94 octane no problem.
when I blew the crappy cometic head gasket I milled the head (again) as far as it could go and kept running 94 octane no problem.
I do have endyn/wiseco rollerwave pistons which are supposed to help but I know guys running CTR pistons with GSR heads (yielding the highest c/r possible with those pistons) and 94 octane without any problems what so ever.
you say you know guys who put holes through the CTR pistons. one of two things:
1. no clearences where checked and the motor blew on start-up
2. over revving the engine or totally miss shifting and having the rpms shoot up to oblivion and beyond
I stick by my privious post: 12:1+ is deffinetly possible on 94 octane. just watch that timing!
15-Apr-2003, 01:35 PM
#20
Guest
Posts: n/a
Camille, it was me that told him! 
cuz you had mentioned the C12 and octane booster on the forums a number of times here and here too so i didn't think it would make any difference. Hope you're not mad at me
Anyways we need to meet up and finish that "little" project we've got going. I've got a new scanner oh and pick up your phone! you're beginning to be like me.
cuz you had mentioned the C12 and octane booster on the forums a number of times here and here too so i didn't think it would make any difference. Hope you're not mad at me
Anyways we need to meet up and finish that "little" project we've got going. I've got a new scanner
oh and pick up your phone! you're beginning to be like me.
