Conference terri::cars_uk

I'am sure someone will put me right here


injection:  Petrol is just injected (sprayed) under high pressure
into the engine

turbo: The exhaust gas from the engine drives a small turbine (pump)
.. this pump is then used to force Petrol into the engine
(which is why you get turbo lag and the turbo only cuts in at
'high' revs)

Supercharger: A pump (as above) _but_ connected to the engine drive..
so there is always an element of Supercharger 'injection' there
... rather than the turbo which cuts in & out
[EOB]

In a "conventional" engine, the suction of the piston moving down the cylinder
pulls air in through the carburettor, where all sorts of physical laws to do
with pressure changes and turbulence suck petrol out of the jets in a fine mist.
The mixture enters the cylinder and I'm sure you know the rest.

The trick is to get the right amount of petrol for the engine speed / load,
which has led to some ingeneous and novel carburettor designs.

Petrol injection is a radical change and does away with the carb altogether.
Petrol is injected directly into the air flow passing through the manifold.
Clever mechanical / electronic wizardry ensure exactly the right amount of
petrol is injected at exactly the right moment.

A turbocharger (and supercharger) deal with the air rather than the petrol.
They forcibly push air into the inlet manifold, instead of the cylinders having
to suck it through, so you can get more air in more quickly.

Scott

In petrol cars, fuel injection is used to spray finely atomised fuel at the
inlet valves.  Some systems do this continuously, others pulse the injectors.
Unlike deisel injection, the spray is not usually timed to the opening of the
inlet valves.  Fuel injection gives better control over the mixture (ratio of
petrol to air) used and also a better atomisation so it gives better performance
than carburettors with better economy.  It is also easier to control a fuel
injection system to meet emmission laws.  Some cheap FI systems only use one
injector to replace the carburettor (eg Rover K series I think).  This is done
to enable the car to meet emmissions rules and to enable the system to be used
with a catalytic converter which requires closed loop control of the mixture.

A turbo charger can be used with FI or carburettor engines.  It is simply a 
turbine driven by exhaust gas which pumps air into the engine.  The FI or
carburettor ensures that the mixture is correct by metering the fuel as
necessary.  A turbo is a relatively cheap way of getting more power from an
engine.

Hope this helps,

Mike. 

>>                      <<< Note 1055.3 by VANDAL::BROWNM >>>
>>Unlike deisel injection, the spray is not usually timed to the opening of the
>>inlet valves.  Fuel injection gives better control over the mixture (ratio of
    
    
    Ahem!. in  diesels the injection is NOT timed to the valves...
    
    	(diesels only follows) 
    The engine on the down-stroke sucks in ONLY air. On the upstroke it
    compresses it around 23:1 thus it gets very hot. Just before top-dead
    diesel is injected directly into either the cylinder itself (so called
    direct injection) or into an ante-chamber open to the cylinder (so
    called indirect or recardo[the guy who invented this chamber]).  This
    fuel ignites spontaneously on mixing with the hot air causing the power
    stroke.  
    	(end of diesels only)
    
    Petrol injection is into the airflow being drawn into the cylinder.
    There are two main sub-divisions: single point and multi point.
    Single point is a fancy carb-replaced-by-injection, there is a single
    venturi (the restricted tube) but instead of the air sucking the
    petrol out of a pin-hole jet as in a carb, it is injected out by a
    pressure/metering system.
    Multi point is where there is a separate injector for each cylinder,
    usually located at the engine end of the manifold.
    
    
    Turbo's, as has been said, deal with pre-compressing the air using
    waste power out the exhaust. This means more air in the cylinder, more
    of a punch out. 
    
    Another term related to turbo's is intercooling. This is located
    between the turbo and the inlet to the engine. As the turbo compresses
    the air it heats up, the intercooler removes this heat, the air gets
    cooler and denser, thus EVEN more gets into the cylinder, thus even
    more punch!
    
    Richard.
    P.S. now you should have 
    a. enough info to go off and impress your girlfriend
    b. so much info your totally lost and won't bother to try to .....
    :-)
    
    PPS. Put at it's simplest, injection is squirting in the fuel, turbo is
    blowing in the air!.

    An Aside to this topic:
    
    Turbocharging is more effective in diesel engines in that there's much
    less 'lag' compared with petrol engines. In petrol engines the revs
    need to be quite high for there to be enough exhaust pressure for the
    turbo, but in diesels were the compression ratio is much higher and the
    exhaust gas temperature is higher then the turbo can operate at lower
    revs... hence less 'lag'.
     Thats why a lot of trucks and buses are turbocharged.
    
    Huw Williams.
     

Re .4:  Thanks for the clarification, Richard.  The point I was trying to make
is that on most petrol injection systems, the timing of the moment when the fuel
is squirted out of the injector is not related to the valve timing;  in many 
systems, the injection is actually continuous and the amount of fuel is 
controlled by the fuel presssure, in others the injectors are pulsed at constant
pressure and the width of the pulse determines the amount of fuel injected.  In 
most of the latter type of systems, the injectors are all fired at the same
time, although in a few they do actually fire sequentially, as they do in all
deisel engines but as you point out, deisel injection occurs near the top of the
compression stroke, not the opening of the inlet valve.

Mike.

A couple of questions about turbo's (should this be in the
"The Incredibly Stupid Questions" topic ? :-) )

(1) what a "wastegate"?.. I guess its just a fancy name
for a (spring loaded?) value that diverts some of the
high pressure air generated by the turbo away (past)
the engine itself.. when the turbo is producing a too
high pressure (so could you increase performance
by raising the pressure at which this value starts to
dump air?)

(2) Boost gauges?  why do you need them ?  sure its 'nice'
to know that your turbo is generating (say) 10PSI..
but wont the boost gauge just mirror the rev counter?
.. IE the more revs you do..the higher the pressure
..(subject to the wastegate dumping air as about)

(3) will my car go faster if It has furry dice
hanging from the rear view mirror ?

    Well, I don't know about 2) but the answer to 1) is that if you didn't
    have a wastegate you wouldn't have an engine!! Left to its own devices,
    if you accelerate an engine with a turbo, you get power returned by the
    turbo which results in increased performance from the engine and more
    revs from which you get more power returned from the turbo from which,
    eventually, you go bang! The wastegate "dumps" excess power to prevent
    the engine overloading - if you fiddle with this you are in danger of
    stressing other components too highly, usually the ones which go bang
    and make a mess of the engine compartment by forming unwanted holes in
    the big metal thing and letting the oil ooze out.
    
    The only reason I can think of when you would need a boost guage is
    when you can vary the boost (as in racing cars) - you take a risk that
    the higher boost will damage the engine but can offset that against
    your chance of glory!
    
    Some cars (eg Lancia Thema) have a sort of built-in, non-adjustable (by
    the driver) "overboost" device which lets the engine, when under hard
    acceleration, boost higher than normal but it only lets it get away
    with it for a few seconds before it dumps the power.
    
    QED,
    	Colin

>>
(2) Boost gauges?  why do you need them ?  sure its 'nice'
to know that your turbo is generating (say) 10PSI..
but wont the boost gauge just mirror the rev counter?
.. IE the more revs you do..the higher the pressure
..(subject to the wastegate dumping air as about)
>>

I think that a boost guage is the LAST thing you'd want to look at if a turbo 
engine was coming on boost...

...art

    In my Renault, I use the boost guage in 2 ways.
    
    a. As a fuel economy meter. Boost on - fuel consumption up. By
    carefully adjusting the accellerator you can kill the boost without
    losing the speed.
    
    b. The proper way - ie it indicates the power available to me. If
    I'm travelling at 40 with no boost (it happens ;-)) I know that
    a sudden overtaking manouver will take a bit longer than if the
    turbo's on.
    
    Rich

    
    A wastegate is in fact used to make pleasant whistling sounds.
    With the correct "right foot technique", a selection of sounds can
    be generated, my favourite being the "falling bomb" or "coyote about
    to land face first at the bottom of the canyon" effect.
    
    Makes passengers, who don't know you have a turbo, wonder what on
    earth is going on under the bonnet !
    
    Gordon
    
    
    	

A boost meter is pretty sexy too.

It is *incredibly* responsive to the throttle, and usually goes up before the
revs do.

Now how do I get these tunes from my turbo?

    re .7
    
    1) The wastegate diverts exhaust gas past the turbo once the max.
    pressure has been reached. This prevents excess pressure and provides
    an easier path for the exhaust gas to flow through, reducing the effect
    of the back pressure on the engine.
    
    2) The boost gauge does not mirror the rev counter. It can go up to
    maximum at any revs that can spin the turbo fast enough (usually any
    speed from somewhere just above 2000). There is no real need for it for
    normal driving, as you can easily tell whether you have any boost or
    not.
    
    Andrew

    Re: .11
    
    On my R5GTt,  i find that the pleasant whistling sound occurs just
    as the boost starts to build up, thus is probably the turbine starting
    to wind up to speed, rather than the wastegate opening.
    
    What car r u driving?
    
    mb

	Re. .14

	Well , while some whistling does occur at the point of turbo boost
	starting to come in, the most prominent whistles are produced when I'm
	easing off on the throttle .

	Oh, and I'm driving a Nissan 200SX.

	Gordon

    During my test of the BX turbo last week, I initially kept thniking,
    "allo, there's a cop car aproaching in a 'urry!".
    
    Then I read this and now I know better!.
    
    Richard

    Most of the whistling in my RS Turbo comes from envious Pug 205 owners (oops
    sorry not that rat hole again)..
    
    Seriously the whistling on mine starts as the turbo starts to produce
    boost at about 2500-3000 RPM between gears I get a popping sound which
    I thought was the wastegate gate opening.
    
    I find driving through tunnels with the windows down produces the best
    sound, but hate having to interupt my musical pleasure for selfish
    un-whistling cars on the same stretch of tunnel that I am trying to
    use.
    
    I would like to increase the volume on my whistle (any suggestions)
    
    
    Regards
    
    
    Bruce
    
    
    Regards
    
    
    Bruce

    
    	It may be (or may not be, of course) interesting to note that
    Turbo-charging a Diesel engine results in a large gain in BHP (around
    50%-ish) and Torque (Around 80%-ish) and a small cost in fuel
    consumption (only 2 or 3%-ish).
    
    	In the case of petrol engines, the amount of power and torque gains 
    are proportionally higher usually, but the cost in fuel consumption is,
    as far as I can see without any experience of it, VERY much higher.
    
    	Anyone with experience of Turbo-charged petrol engined cars care to 
    comment?
    
    			Malcolm. A BX TZD Turbo driver until August. 8-)))

    I get about 32-33 Mpg from my Renualt 21 Turbo Driving it just 2.L
    injection and about 26 Mpg Driving like a man possessed ..!!
    
    
    
    
    Steve