satburn

Some interesting reads:



http://www.dragtimes.com/forums/index.php?showtopic=205

...and the thread that Randy was talking about

https://www.dieseltruckresource.com/...ad.php?t=63642

Duallydog

Here's an idea I had been thinking about for awhile. What if you took a turbo charger and instead of running on a common shaft you hooked up basically an alternator to the exhaust side and used an electric motor to run the compressor side?

qmcdt

So what some of you are saying is that if you take the roots blower off a two stroke and put it on a 4 stroke it becomes supercharger? I'm sure the timing in the two stoke diesel, between the time the intake ports are uncovered and the exhaust valves close, allows the roots unit to scavenge the cylinders and then build pressure in the cylinders above atmospheric pressure, thus supercharging said cylinders. (Look at the Summit website and see that they call them 6-71, 8-71 and 12-71 roots type supechargers. All from the detroit diesel series of two stroke engines of the same designations.) Weither or not one is using an exhaust gas driven centrifical blower (turbo), a belt driven rotary lobe blower (roots) or a helicly cut axial flow screw type blower (whipple/et al), stuffing more air into the cylinders, with or with out added fuel will increase cylinder pressure and thus power output. The belt/gear driven positive displacement types, output at a linear rate and can make boost at idle where the turbine driven type can't. (they run out of boost as the engine they are flowing into comes into it's dynamic flow zone and can out flow the blower.) Until exhaust gas flow and temperature are high enough to drive the unit, the turbine driven blower acts like both a throttle and an exhaust restriction. Put a supercharger (woops a belt driven positive displacment type blower) on any diesel engine that smokes at idle and the smoke will go away. (Until the fuel gets turned up more that is. Take the blower off a 2-stoke and it will smoke like a pig at idle, if it will even start) So, all poopyness aside, shoveling more air into your engine with any type of air mover (positive displacement types for bottom end performance and turbine driven types for top end performance), or even a can of pressurized stuff that has oxygen in it, will help it make more power, as will boring and stroking the engine itself. If I offened anyone with my mistatement of device nomenclature, I appoligize. For the rest you, bolt it on if that's what you need, or like, or are brave/crazy enough to try it, and then come tell us your results here please. More is better, and you can't make an omlette if you walk lightly on the eggs. Stomp around on them and then use a strainer to get the shells out. Sorry for ing here, but like Nike used to say, Just Do It. (then tells us about it after)

RustyJC

Precisely. That's why it's called a Roots blower. It's there merely to scavenge the 2-cycle engine in place of the missing exhaust and intake strokes. Without it, the engine would not run. Our 2-cycle engines that utilize blower scavenging have centrifugal blowers that are gear-driven off the crankshaft at 20 times engine speed.

For an engine to be supercharged, cylinder pressure at the initiation of the compression stroke must be significantly higher than atmospheric pressure. 2-cycle engine port timing (in the case of a loop-scavenged engine) and/or exhaust valve closing (in the case of a uniflow engine) prevents this from being the case when only scavenging air blowers are used. When a turbocharger is added to the scavenging air blower, however, the exhaust back pressure created by the turbocharger allows the cylinder to be "packed" with air (supercharged) yielding an initial compression pressure significantly above atmospheric pressure.

The difference between a "blower" and a "supercharger" is the discharge pressure of the device. When applied to a 4-cycle engine, because the exhaust valve(s) are closed when most of the intake event is taking place, the blower can be used to pack the cylinder with air, and it becomes a supercharger.

It's a subtle point, but to us engineers, it's one worth making.

Rusty

Ironstone

I saw a detroit inline 6 on ebay a while back. It had the scavenger system/blower and turbos. I think it came out of a tandem. It sold pretty high. It all looked stock to me. Nice looking engine though. I want to say it was a 6/71 but im not sure on that.

Red3quarter

I know they are called roots blowers, and i know that a supercharger is different but some guys in the field will refer to them as a supercharger. You just can't break some of the older guys from calling things one name or doing things differently, when they call it a SC i don't argue because they think its right.

NoSeeUm

I am curious now, scavenge as in the blower is connected to the exhaust side pulling vacuum on the cylinders?

Jim

RustyJC

Jim,

No, the blower is used to scavenge the cylinders by forcing air through the cylinders from the intake, through the cylinder and out the exhaust. Remember, the 2-cycle engine does not have an exhaust or an intake stroke, so they use this scavenging cycle when (in the case of a port-scavenged engine) both the exhaust and inlet ports are open. During that scavenging cycle, fresh scavenging air is pushed from the air manifolds through the inlet ports, through the cylinder (sweeping out the residual exhaust gas ahead of it) and out the exhaust ports. Scavenging air flow on a non-turbocharged engine is generally around 130% to 150% of engine displacement.

Rusty

NoSeeUm

OK thanks.

I am used to talking about scavenge in terms of components that pull from the downstream side. EX: Scavenge oil pumps or the tuned exhaust pipe on alot of 2-stroke gas engines etc...

Jim

Ph4tty

Is there an automotive alternator that will turn at 100k rpms? Dunno about that part of the idea, but I do like the idea of an electrically assisted turbo. Something that could bring up the rpms of the turbo then disengage.

Equalizer 2

Back in the 1930s Cummins entered a few races at Indy and one year entered a diesel with both a supercharger and turbo. This may have been a two cycle engine as they entered one in one of the races I believe they also had a 4 stroke in this race. If I recall correctly the two cycle gave Cummins the best finish of any race he entered. For early technology in the diesels they did quite respectable finishes. The rules were of course that no matter what they could not be the actual winner. They also entered an aluminum engine in one of the races and when they shut it down it totally siezed up.

I believe they also ran a couple of races at Indy in the early 1950s.

Artsi_L

Cummins at Indianapolis 500

jughead

"This year will go down in history. For the first time, a civilized nation has full gun registration! Our streets will be safer, our police more efficient, and the world will follow our lead into the future." --Adolf Hitler, 1935
not a flame but i think i read somewhere that that quote is bogus. i am not a hitler fan either. if i am wrong please correct me

apwatson50

I believe that this has been done before, i'm sure if you google searched you could find something.

"Here's an idea I had been thinking about for awhile. What if you took a turbo charger and instead of running on a common shaft you hooked up basically an alternator to the exhaust side and used an electric motor to run the compressor side?"

This would be much less efficient. You loose efficiency creating the electricity, then you loose again turning the electricity back into work.

Deezle98

Yup, if it aint broke dont fix it!