Dave Baker
2012-02-23 12:46:21 UTC
After reading some of the gibberish in the "2014 fuel flow and low down
torque" thread I thought I'd better post what's really happening with this
engine in a new thread rather than let any comments get lost in the
squabbling.
The mandated engine is a single turbo V6 of 1600cc capacity and a maximum
80mm bore size. This in turn sets the stroke at 53mm if they use the full
bore size allowed and the bore stroke ratio at 1.51 which is not very
oversquare for modern F1 engines. In fact it's not an unusual ratio for
standard road car engines and motorbike ones.
Fuel flow is limited to a maximum rate of 100kg/hr from 10500 rpm upwards to
the 15000 rpm rev limit and below 10500 it decreases in a linear fashion
with rpm down to idle where there is just enough fuel flow to keep the
engine running.
In a normally aspirated engine with unlimited fuel flow the engine's power
is airflow restricted. The better it can breathe, and at the highest
possible rpm the more power it can produce and this is essentially a
function of total inlet valve area. With a turbo engine the addition of
boost pressure can multiply this power up to almost any factor, limited only
by detonation and the physical strength of the engine components. This led
to 1500cc engines producing up to 1500 bhp in qualifying trim in previous F1
seasons.
With fuel flow limited however the engine's power output is also limited and
becomes a function of the Brake Specific Fuel Consumption (BSFC) that can be
achieved. No matter whether N/A or forced induction this bhp limit will be
about the same. A conventional petrol road car engine running stoichiometric
fuel/air mixtures mandated by the catalytic converter can achieve a BSFC in
the low 0.4s lb/bhp/hr. Race engines running richer fuel mixtures at higher
rpm with greater frictional losses struggle to achieve better than about 0.5
lb/bhp/hr.
If by careful design the F1 engine designers can get anywhere close to the
BSFC of a road engine of say 0.43 lb/hp/hr we can calculate that the 100
kg/hr fuel flow limit will limit power to about 510 bhp from 10500 rpm
upwards. If they can't achieve a BSFC that low then obviously power will be
less too. We'll have to see how they get on but clearly they will not be
able to get anywhere near the current 750 bhp as some have incorrectly
surmised.
At lower rpms as the fuel flow limit reduces then the power will also reduce
in a straight line fashion to generate a power curve that looks similar to
that of a normally aspirated engine where power at any rpm is a function of
torque x rpm. This has been done very deliberately to prevent designers
using very high boost pressures at low rpms to create an engine with 510 bhp
everywhere in the rpm range.
We can now calculate the boost pressures that will be required to fully
utilise the fuel flow limit. A normally aspirated 4v F1 type race engine on
conventional petrol is limited to producing about 97 ft lbs of torque per
litre. This indicates about 155 ft lbs from a 1600cc engine at peak torque.
At 10500 rpm this would set power at 155 x 10500 / 5252 = 310 bhp. However
there is sufficient fuel flow for 510 bhp so the turbo boost factor required
will be 510 / 310 = 1.645.
Boost factor = (atmospheric pressure + boost pressure) / atmospheric
pressure or (14.7 + B) / 14.7.
If (14.7 + B) / 14.7 = 1.645 then B = (1.645 x 14.7) - 14.7 = 9.5 psi
At 15000 rpm at the same torque value the N/A power equivalent will have
risen to 155 x 15000 / 5252 = 443 bhp
As fuel flow is still limiting power to 510 bhp the boost factor required
has fallen to 1.151 and we can calculate that the boost pressure required
has dropped to only about 2.2 psi.
All of this ignores some unavoidable flow and efficiency losses created by
the turbo itself and the associated pipework, intercooler etc and by the
need to run lower compression ratios than for a N/A engine. It also does not
account for the fall in torque produced either side of the peak torque rpm
but allowing for everything it is unlikely that a well designed engine will
need to run much more than about 11 or 12 psi of boost pressure up to 10500
rpm and then steadily decreasing from this down to maybe 4 psi at 15000 rpm.
These are not high pressures, even for a road car engine, and will not
require anything very special in the engine design to accomodate. With the
relatively low rev limit of 15000 the engines should be very reliable and
long lasting. It's possible that with development such an engine could go
most of a season or at least well into it. Any loss of power due to wear and
tear can be corrected for by increasing the boost pressure to continue to
use the fuel flow limit to its full.
So the design constraints of this engine will be very different from that of
the normally aspirated engines. Instead of concentrating solely on trying to
maximise airflow through the cylinder head to get more bhp the designers
will be trying to optimise fuel efficiency (minimise BSFC) and minimise
frictional losses as they can get the power they want, or that the fuel flow
limit restricts them to, simply by changing the boost pressure. Using the
highest possible compression ratio without detonation at the required boost
pressures, creating the fastest possible burning combustion chambers and
achieving fuel droplet distributions that burn at the leanest possible
fuel/air ratios will be their challenges.
They should be able to achieve 450 bhp very easily. Whether they can get 510
or even beat that is more doubtful but I suspect that their research will
have valuable knock on effects for road engine design in due course. I'll be
surprised if they haven't hit 500 bhp by the time the engines need to be
used.
torque" thread I thought I'd better post what's really happening with this
engine in a new thread rather than let any comments get lost in the
squabbling.
The mandated engine is a single turbo V6 of 1600cc capacity and a maximum
80mm bore size. This in turn sets the stroke at 53mm if they use the full
bore size allowed and the bore stroke ratio at 1.51 which is not very
oversquare for modern F1 engines. In fact it's not an unusual ratio for
standard road car engines and motorbike ones.
Fuel flow is limited to a maximum rate of 100kg/hr from 10500 rpm upwards to
the 15000 rpm rev limit and below 10500 it decreases in a linear fashion
with rpm down to idle where there is just enough fuel flow to keep the
engine running.
In a normally aspirated engine with unlimited fuel flow the engine's power
is airflow restricted. The better it can breathe, and at the highest
possible rpm the more power it can produce and this is essentially a
function of total inlet valve area. With a turbo engine the addition of
boost pressure can multiply this power up to almost any factor, limited only
by detonation and the physical strength of the engine components. This led
to 1500cc engines producing up to 1500 bhp in qualifying trim in previous F1
seasons.
With fuel flow limited however the engine's power output is also limited and
becomes a function of the Brake Specific Fuel Consumption (BSFC) that can be
achieved. No matter whether N/A or forced induction this bhp limit will be
about the same. A conventional petrol road car engine running stoichiometric
fuel/air mixtures mandated by the catalytic converter can achieve a BSFC in
the low 0.4s lb/bhp/hr. Race engines running richer fuel mixtures at higher
rpm with greater frictional losses struggle to achieve better than about 0.5
lb/bhp/hr.
If by careful design the F1 engine designers can get anywhere close to the
BSFC of a road engine of say 0.43 lb/hp/hr we can calculate that the 100
kg/hr fuel flow limit will limit power to about 510 bhp from 10500 rpm
upwards. If they can't achieve a BSFC that low then obviously power will be
less too. We'll have to see how they get on but clearly they will not be
able to get anywhere near the current 750 bhp as some have incorrectly
surmised.
At lower rpms as the fuel flow limit reduces then the power will also reduce
in a straight line fashion to generate a power curve that looks similar to
that of a normally aspirated engine where power at any rpm is a function of
torque x rpm. This has been done very deliberately to prevent designers
using very high boost pressures at low rpms to create an engine with 510 bhp
everywhere in the rpm range.
We can now calculate the boost pressures that will be required to fully
utilise the fuel flow limit. A normally aspirated 4v F1 type race engine on
conventional petrol is limited to producing about 97 ft lbs of torque per
litre. This indicates about 155 ft lbs from a 1600cc engine at peak torque.
At 10500 rpm this would set power at 155 x 10500 / 5252 = 310 bhp. However
there is sufficient fuel flow for 510 bhp so the turbo boost factor required
will be 510 / 310 = 1.645.
Boost factor = (atmospheric pressure + boost pressure) / atmospheric
pressure or (14.7 + B) / 14.7.
If (14.7 + B) / 14.7 = 1.645 then B = (1.645 x 14.7) - 14.7 = 9.5 psi
At 15000 rpm at the same torque value the N/A power equivalent will have
risen to 155 x 15000 / 5252 = 443 bhp
As fuel flow is still limiting power to 510 bhp the boost factor required
has fallen to 1.151 and we can calculate that the boost pressure required
has dropped to only about 2.2 psi.
All of this ignores some unavoidable flow and efficiency losses created by
the turbo itself and the associated pipework, intercooler etc and by the
need to run lower compression ratios than for a N/A engine. It also does not
account for the fall in torque produced either side of the peak torque rpm
but allowing for everything it is unlikely that a well designed engine will
need to run much more than about 11 or 12 psi of boost pressure up to 10500
rpm and then steadily decreasing from this down to maybe 4 psi at 15000 rpm.
These are not high pressures, even for a road car engine, and will not
require anything very special in the engine design to accomodate. With the
relatively low rev limit of 15000 the engines should be very reliable and
long lasting. It's possible that with development such an engine could go
most of a season or at least well into it. Any loss of power due to wear and
tear can be corrected for by increasing the boost pressure to continue to
use the fuel flow limit to its full.
So the design constraints of this engine will be very different from that of
the normally aspirated engines. Instead of concentrating solely on trying to
maximise airflow through the cylinder head to get more bhp the designers
will be trying to optimise fuel efficiency (minimise BSFC) and minimise
frictional losses as they can get the power they want, or that the fuel flow
limit restricts them to, simply by changing the boost pressure. Using the
highest possible compression ratio without detonation at the required boost
pressures, creating the fastest possible burning combustion chambers and
achieving fuel droplet distributions that burn at the leanest possible
fuel/air ratios will be their challenges.
They should be able to achieve 450 bhp very easily. Whether they can get 510
or even beat that is more doubtful but I suspect that their research will
have valuable knock on effects for road engine design in due course. I'll be
surprised if they haven't hit 500 bhp by the time the engines need to be
used.
--
Dave Baker
Dave Baker