>you are comparing apples to oranges....... when given the same engine,
>the turbo version will always have more power... we are talking about
>diesel engines, not gas or other fuels. with diesel, fuel = hp. the
more
>you can burn on the power stroke = more power and to burn more fuel you
>need more air.
>
Tom is quite correct but there are some areas of possible
misunderstanding.
Supercharged diesels, weather it be by turbine or mechanical means, will
produce slightly more power owing to the increased CR and the extra air
available for combustion with the _same_ fuel injection setting.
To take advantage of the extra air available the injection pump needs to
have a signal from the inlet header of the boost pressure to tell it to
inject extra fuel or else you get a momentary but huge cloud of black
smoke when demanding full power before the turbine winds up as the
engine is effectively grossly over fuelled.
When overhauling a diesel or indeed at a respectable mileage it is worth
having the injection pump serviced and re-calibrated at a specialist
shop. The max fuel setting usually drops with use and although you may
have the pedal on the floor in reality the injection might only be
equivalent to 3/4 power or so. The shop will want to know exactly what
engine the pump is used on to precisely set the full power fuelling
demand.
There are exceptions, some engines owing to size or layout (Detroit
Diesel especially), have a separate and individual combined
pump/injector for each cylinder operated by a "third" rocker arm and
cam, this is normally found on larger engines where the pipework from a
centralised pump would be excessively long causing a delay in the
injection point and loss of pressure owing to the elasticity of the
steel pipe; which is why the injection pipework is often seen to be bent
up to make the overall lengths equal between the nearest and farthest
injector.
Injection pumps are most critical items and usually made by a
specialist company, never be tempted to get inside one or remove the
often fitted lead seals as many shops will not accept a unit with
broken/missing seals, their test and calibration rigs cost tens of
thousands of dollars/pounds and they will not risk it with a tampered
pump.
Not everything that looks like a blower is a supercharger, the industry
makes a subtle but important distinction between supercharging and
scavenging; broadly engines with inlet manifold (header) pressures in
the 0 to 1 psi range are scavenged whilst above that are supercharged,
its a question of what the cylinder pressure is at the beginning of the
compression stroke.
Two-stroke (two-cycle) diesels are generally scavenged, the big,
tri-lobe blower nestling in the V of a Detroit Diesel does no more than
fully purge the cylinder of residual waste gas, being a two-stroke there
is no piston exhaust stroke to effect this. Generally all the
two-stroke designs are scavenged, right up to the "cathedral" diesels
found in super-tankers of some 300,000 tons, so called as they are
cathedral sized ! The two-stroke diesel has a serious advantage over
more regular types by firing twice as often at the same crank revs as a
similar sized four-stroke with the obvious result.
Richard
(Southampton UK)
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