Diesel design history

[TomC]

On locomotive EMD (Electro Motive Diesel) on series 567, 645 and 710, they are just like giant engines to our bus engines. What makes them unique is the mechanically driven turbocharger with over ride clutch. When the engine is at idle, the clutch engages and the engine spins the turbocharger to maintain proper boost. When the engine accelerates and the boost starts, the turbocharger rises in RPM faster then the engine is driving it and it turns into a normal turbocharger (think of a bicycle). Hence EMD's are very fuel efficient-so much so most all railroads outside of California prefer the 710 series (not smog approved in California anymore). Good Luck, TomC

[Dreadnought]

Even amongst supercharging there are different types.

The ones I've had most development experience of- have been the Roots type positive displacement types.

The luxury sports/coupe/saloon I helped design/develop in the UK used an Eaton M112. The beauty of this device on a petrol engine- is that it does no internal compression work. This means it can be bypassed at part load and the losses incurred are minimal- like the parasitics of an alternator. At WOT full load- on a 4 litre engine it will consume about 70 bhp. It consists of 3 lobes that are twisted through 60-90 degrees ( I don't rememeber how much exactly).
The Gen 5 of this device used an abladable composite coating to get the tolerances tight and the seal to further increase the efficiency.

But the best improvement was the latest iteration of this- the TVS blower- which uses quad lobes that twist through 160 degrees. This unit similarly can be bypassed but its peak efficiency is up at 60-70% compared to the M112s 55% ish. This ensures the tank temps have lower temperatures and parasitics are better.

I do intend to get one of these TVS on my Jaguar one day and continue the work I did as a young man!

The other type of supercharging often consists of something akin to a small compressor like that found on a turbo charger (rotrex for example) - this DOES internal compression work. Similar to this is a Lysholm compressor- again- consisting of a male and female rotor- it DOES internal compression work and therefore bypassing wont reduce parasitics. In the past these units were always more efficient than the old M112 Super chargers, but now with the advent of the TVS units, the difference is small and there's the added disadvantage of bypassing giving nothing.

The other advantage of a positive displacement device like the Eaton Roots style blower- is that their air charge/boosting response to the throttle is pretty much linear- which feels like a big big engine- this isn't the case with the turbo style Rotrex for example.

As has already been covered- a diesel engine is a different animal to a petrol- it is effectively pretty much running at full airflow (like a petrols WOT) always- but the load is moderated by the injected fuel amount. Therefore a Super charger on a diesel will always incur a parasitic loss.

Out two strokes NEED a positive displacement pump of some form of boost- as the piston doesn't suck to bring in fresh charge. You will notice that going from the 8v71 to the 8v92 Detroit actually did what they could to drive the super charger less hard and rely on the turbo more- again to bring down parasitics.

Tom C I have a friend who works for EMD- he swears by the two stroke.

He's a young chap, from Germany, very data driven and has no bias either way, but believes the 2 stroke EMD is here to stay....

I had assumed originally with the acquisition of EMD by CAT, that they would force one of their 4 stroke leviathons on EMD but it may not pan out that way afterall...

[luvrbus]

Looks to me like the older technology is finding it way back into engines the Cat C8.7 uses the supercharger and turbo inline like some models of the old NH and Kta Cummins engines of the 70's.
FWIW EMD was building the 4 stroke EMD engines 5 years before it was sold to Cat,they even had a CNG version .EMD engines run a DC generator it is nothing like a automotive type engine, they are not cast each piece is welded together .You see lots of CNG fueled  CAT and EMD engines pass through Needles along with the diesel fueled engines       

[Jeremy]

    No, the DD two-stroke system is different from the configuration used on, say a two-stroke motorbike or a chain saw.  In the other systems, the crankcase is used as a pump, air is drawn into crankcase and fuel metered along with the air (and usually oil is metered, too), then when the piston is traveling downward, the air/fuel mixture is pushed from the crankcase into the volume above the piston.  This is the positive pump action for these systems and ports - at different levels on the cylinder to control timing - allow for transfer and exhaust. 
    On the DD two-stroke, there is little timing effected by the intake ports - when the piston is low, they're open.  The exhaust is controlled by valves in the head (like ordinary 4-stroke poppet valves).  To fill the cylinder with air (fuel comes later), there has to be positive pressure blowing fresh air in near the lower part of the cylinder.  The timing comes from the exhaust valves.  Once enough air has been injected to scavenge the cylinder of exhaust gases, the rising of the piston closes the intake ports and begins the compression phase of the cycle.
    So it's this "flow-through" aspect of the DD two-stroke system that requires positive pressure to help blow out burnt gases through the exhaust and fill the cylinder with fresh air; it's the "blower" that does this.

(Somewhat simplified for brevity, but that's about right.)

HTH and FWIW,  BH etc.

Thanks for that; I was vaguely aware that the ports and valving arrangements were entirely different but I've never sat down studied how the cycle works on a DD 2 stroke - and I'm one of those people that is always slightly surprised when reminded that the Otto cycle isn't the only game in town. Just the other day I was watching a video on Youtube of a (petrol) IC engine configuration that had extra 'low pressure' cylinders working off the exhaust gas, just like a compound steam engine - which I suppose in many ways is an alternative to a turbo as a way of increasing output by extracting energy that would otherwise be wasted down the tailpipe

Jeremy

[uncle ned]

2 stroke engines.

I have a single cylinder engine from a motorcycle that has 2 pistons on a y shaped rod.

It is referred to as a twingle.

The front piston sets on the exhaust port.
the back piston sets on the intake port.

Years before exhaust chambers to control the back pressure.

uncle ned

[Iceni John]

Didn't Detroit make a short-lived 51-series engine that was valveless?   it used intake and exhaust ports in the cylinders?   I assume it still needed a scavenge blower.

Yes, other engine designs are fascinating.   I was reading about a 5-stroke engine  -  is that the compound style that was mentioned?   There was a significant increase in efficiency when steam locomotives adopted compound cylinder arrangements.

(Talking of steam locos, did you send the recent video of Tornado achieving 100 MPH?   Tornado is a modern replica of a LNER Pacific loco, built just a few years ago using modern techniques such as a fully-welded boiler, and it's being tested for its suitability to run mainline trains at 90 MPH in Britain.   Sometimes the distinction between old and new blurs.)

John

[Jeremy]

Yes, the 'compound' petrol engine is described as a 5-stroke - as I say there are videos of the configuration on Youtube, although the one I saw was only of a cutaway to show the operation - I'm not entirely sure whether it's still just a concept at this stage or if running examples exist.

And Tornado is certainly cool, although it's a Peppercorn class rather than a Pacific class incidentally. There's another steam loco already in regularly-scheduled mainline operations here now as well, and the heritage steam scene in the UK generally is absolutely huge (I sell the magazines that cover it!). It's especially big in Germany too I believe, and they've been developing and building 'modern' steam locos there for years which are just worlds-away from the coal-fired heavy-metal dinosaurs that everyone thinks of when you say 'steam'

Jeremy

[Oonrahnjay]

2 stroke engines.

I have a single cylinder engine from a motorcycle that has 2 pistons on a y shaped rod.   It is referred to as a twingle. ...
uncle ned

    Sachs (F&S), Ned??