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can you please explain. I cannot see any relationship between compression ratio and fuel consumption.So, yes - DB-601 was more fuel efficient than Merlin. But, not because of fuel injection, but because of notably higher compression ratio?
can you please explain. I cannot see any relationship between compression ratio and fuel consumption.
cimmex
Sounds reasonable but I don't buy it. It would be far easier to increase the CR than improve the charger to get more boost. I wonder why RR didn't go that way.Higher CR means less boost required from the compressor, thus less power expended in driving the compressor, thus less fuel used for the same (or more) power output.
Well, power wise both contemporary engines were rather close. IMO the DBs offered some advantages.
Inverted V-design offered better view over the nose,
fuel injection ensured supply at all flight situations,
hydraulic supercharger drive was more efficient,
side mounted supercharger allowed an engine cannon.
cimmex
can you please explain. I cannot see any relationship between compression ratio and fuel consumption.
cimmex
Sounds reasonable but I don't buy it. It would be far easier to increase the CR than improve the charger to get more boost. I wonder why RR didn't go that way.
cimmex
Sorry, cannot see any hint in SR's post that higher CR lowers the fuel consumption.SR6 explained that well.
RR was of opposite opinion - they 1st improved Merlin's supercharger with Merlin XX in 1940, then introduced two-stage supercharger with Merlin 60, already in second half of 1941 in token numbers.
I've done the same, but if you modify a engine to make more power, and you use that additional power, then of course your fuel mileage goes down.Increasing the CR at car engines by skimming the cylinder head was a common tuning action in my youth. We got some more power but I never noticed a lower consumption, mostly higher.
cimmex
Which engine was better the Merlin or DB601? From what I can tell the Merlin had a lower displacement, but the same weight (roughly) as the DB; why was that? What did the Merlin have that made it capable of the same or better HP at lower displacement than the DB?
Allison could be overhauled in the field, while the Merlin, DB and Jumo could not.
Modern aircraft and tank engines are designed to be quickly replaced in the field. Removed engine is shipped back to factory or rear area depot for rebuild. If WWII era U.S. Army rebuilt engines in a field environment then our operational doctrine was behind the times.
Sometimes authors get misled by simple numbers. I have no doubt that a R-R Merlin had more total "parts" than some other engines but many of these "parts" were screws and bolts used to hold thing together or on the engine. Rolls-Royce, even on their cars, liked to use more small screws/bolts spaced closer together to hold on things like cam covers than many other manufacturers. Lets face it, with a V-12 engine there are only 12 pistons now matter who makes it, there is only one crankshaft and so on. Things were you can get more parts are in the valve train. Merlins used 4 valves per cylinder but so did some other V-12 engines, triple vs double valve springs? A more complicated oil pump or more of them? German fuel injection used way more parts than the British carburetor.
DB roller bearing connecting rods used 72 rollers per pair of connecting rods and so on.
With out a meaningful break down of the number of critical or even just "moving" parts the "total" number of parts actually doesn't tell us much about the reliability of an engine although it may tell us a bit about how hard it was to overhaul. Having to deal with a significantly higher number of fasteners could be a pain in the butt even if they make no real difference to the life of the engine.
There are any number of text books about engine design that go into compression ratio. Many from the 1930s and 40s can be found online for $10-20 ALL of the ones I have seen say that higher compression will give better gas mileage or fuel consumption. In some case they will give the result of tests done on test stands with the engine connected to a dyno. Sometimes they have charts/graphs showing the theoretical increase in power by changing the compression ratio with everything else staying the same. Theory and formulas were sometimes backed up by experiments like ones for friction and pumping losses in which a test engine was spun by an electric motor with various parts removed to find out what each part or group of parts contributed to the total friction. Bare crankshafts were spun in the main bearings, "L" head cylinder head was removed to measure crankshaft and piston/ring friction without compression. Power to run fan and so on.
I think I will take their word for what was going on inside some of these engines.