US fuel is very different to ours - not just in the octane rating (we use RON, they use the average of RON and the lower MON - their 89 is about the same as our 95) - but in the list of stuff they have in. Yep, E10 is the default over there, but they get all sorts of chemically aggressive weirdness like oxygenated fuel.
They get E85 widely available, too - as do some European countries, especially Scandinavia.
In message , The Natural Philosopher writes
I drive one handed!
Most field work the other hand is needed for some other task but it has become a habit on the road. The spare hand is usually near the gear lever or hand brake. I do worry that a severe pot hole might lead to an unplanned swerve.
No, just compression of the impounded air. There is no 'fuel/air mixture' as such. The fuel is sprayed into the cylinder at very high pressure to overcome the 'back pressure' of the compressed and heated air where it is immediately ignited on contact with the air, burning continuously in a manner analogous to the flame you get by igniting the spray from a can of aerosol hair lacquer spray (or the way fuel is burned in a jet engine's combustion chamber).
I don't know the exact details for typical high speed diesel engine injection timings but, afaicr, the injection can start in advance of TDC at higher revs and continues spraying for something like 50% of the power stroke, give or take 25% or so.
Unlike a petrol engine, diesels, of necessity, don't throttle the incoming air supply (other than perhaps under exceptional circumstances) so at low power demand, less fuel is required to generate the heat required to cause the working fluid to generate the required working pressure to drive the piston to generate a similar low level power demand of its petrol engine counterpart which has to burn more fuel to generate higher temperatures in order to get the same driving force out of its throttled charge of fuel *and* air. There's much less 'working fluid' to absorb the heat energy and convert it to useful work at fractional power output settings in a petrol engine.
In extremis, when the engines are simply 'ticking over', the power equivalent diesel engine will burn far less fuel than its petrol engine counterpart.
Indeed. Which is precisely why the timing of the injection is so important on a diesel.
but there is no electrical ignition circuit.
Nobody ever said there was.
Ah, I'd assumed that the fuel/air mixture was ingested on the downstroke, followed by the upward compression stroke which by compressing, heated the air until it reached ignition temperature. Was that never the case then - did diesels always have injectors?
To the best of my knowledge, diesel engines have "always" (*) used injectors to define the timing of the ignition.
So to put the issue of timing to bed:
- petrol engines draw fuel-and-air mixture into the cylinder on the induction stroke and ignite it by a spark which is timed to occur just before top dead centre; I believe some engines have a second spark during the power stroke to ignite any unburnt fuel; the fuel-and-air mixture used to be mixed in a carburettor and the fuel is now injected into the inlet manifold; they always have a precisely controlled proportion of fuel to air.
- diesel engines draw air into the cylinder, compress it to about 30:1 compression ratio (unlike about 7:1 for petrol) which causes it to heat up to a temperature at which fuel will ignite on contact; shortly before TDC the fuel is injected and this injection may continue for part of the power stroke; they always have an excess of air relative to fuel.
So the spark of the petrol engine and the injection of the fuel of the diesel engine both determine the "timing" of the engine in the same way.
For both types of engine, the air may be sucked in at atmospheric pressure (normally-aspirated) or may be blown in at more than atmospheric pressure by a turbo- or supercharger. Turbo/super chargers fit more than the rated capacity of air into the cylinder, so allowing more fuel to be injected and thus giving an increase in the effective capacity of the engine.
(*) Ignoring possible variations in early development engines.
Higher than that - 10:1 isn't that unusual in a petrol. Hell, even Land Rovers were using 8:1 in the '60s, unless they were for a country where petrol was about the potency of a damp fart.
Yup
And these days, lower than that for a diseasel. High compression produces NoX in the exhaust, one of the diesel nasties.
In fact Mazda are using 14:1 for both engine types!
Andy
well of cpurse you are talimng direct njection.
Earlier diesels injected fuel into the inlet manifold and it was that fuel air mixture that got compressed and went bang...
Oh and glow plugs play no part ion a diesel that is running.
C0old start only.
Yes and no.
Manifold injection has nearly always been the case, but cylinder injection is fairly new.
Nope. Tractors often use(d) manifold injection.
Except that fuel injection will be a short while before actual ignition
Wrong.
Manifold injection, if it ever existed for diesels, has almost never been the case. Indirect injection systems into a pre-combustion chamber (one per cylinder) was the the common method up until about 10-15 years ago (in cars) as it was easier to make this design quieter and smoother. Direct cylinder inject has overtaken it though with the development of higher pressure injection systems and better control of the injection system.
Direct injection systems though have been around for donkey's years in commercial vehicles where the noise and harshness was less of an issue, but economy more important.
Tim
Diesel doesn't atomise like petrol so a carb wouldn't work.
And even earlier diesels had direct injection. Before WW2.
Unbelievably invented by FIAT, but sold for a song to Bosch ....
Was very common as part of a *real* service to open the carb and find an immiscible drop or two in the bottom.
well technically model aircraft diesel engines are diesels in that they run as carburated compression ignition engines. However they run on paraffin oil and ether mixtures, with the ether doing the main job of ignition.
I don't think I've ever seen a diesel that ran on 'diesel' fuel with a carburettor but I *may* have seen a paraffin engine with a carb - think it was started with petrol and a glow plug..cant remember..
...here ya go/. Original tractor design of engine with carburettor.
Once its hot enough to vapourise the actual paraffin, then it works. Bit like a primus.
Hmm they seem to use spark ignition. I am sure there are some full size tractors using carburation from back in the day..nope. Wiki says not.
Always have been injected apart from model aircraft ones that use ether to get compression ignition going
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