2 stroke thread (with occasional F1 relevance!)

[manolis]

Hello all.


QUOTE from http://www.honda-museum.com/tag/activat ... ombustion/ :


In 1995 Honda re-entered the Paris-Dakar with a bang. The EXP-2 was a radically new and different motorbike, equipped with a revolutionary 400ccm two-stroke engine. After two weeks of racing the african dessert Jean Brucy finished 5th overall and first place in the under-500ccm class.



The EXP-2 was designed to increase fuel economy, drastically reduce emissions and improve torque characteristics over existing two-strokes. The ARC termed system (Activated Radical Combustion) featured fuel injection and a variable exhaust valve which produced controlled auto-ignition at low to medium throttle settings (at high throttle settings the ignition was controlled by a spark plug). The effect was a thoroughly combustion at low revolutions, whereas in a conventional two-stroke engine unburnt gases would escape into the atmosphere.

A linear and wide powerband was the result, giving the EXP-2 a similar performance to its four-stroke competitors – but a substantially better fuel economy and lower emissions. By increasing the mileage of the bike, it could be raced carrying less fuel, which improved handling and decreased rider fatigue.


Track record of the EXP-2:

1995: Rally Granada-Dakar: 1st place in the >500ccm class, 5th overall

1995: Baja 1000: 1st place in class 30, 7th overall

1995: Nevada Rally: 1st place in the class A3 (2stroke >251ccm), 8th overall

End of QUOTE


Honda abandoned their EXP-2 project for some reason.

The common sense says: for some technical reasons and not for marketing reasons.

Because Honda, the biggest motorcycle maker, “manipulates” the market and has millions of fans.




More or less the same advantages are claimed for the Orbital 2-stroke direct injection engines in the Engine Expo 1995 presentation, Hamburg Germany, at http://www.4x4brasil.com.br/forum/attac ... ngines.pdf .




Similar advantages were using in Bimota for their 500cc V2.




The following are from the:
“Revolutionary High-Efficiency Engine-Too Good to be True?”
discussion in the “Tdi club forums” at: http://forums.tdiclub.com/showthread.ph ... 78&page=14


February 25, 2017, DrSmile:

“Epitaph to this thread.... as I prognosticated, not only did this (i.e. The OPOC engine of EcoMotors) never go anywhere (except pull money out of rich men's pockets) in 12 years but the Ecomotors website seems to now be unofficially dead. It joins the ranks of the algae diesel company Solazyme, the Zeroshift transmission, and the Revetec controlled combustion engine.”


And here is the first post in the same discussion:


Wxman, April 13, 2005:

“FEV Shows High-Efficiency 2-Stroke Diesel

By Bill Visnic

WardsAuto.com, Apr 12 2005

Engine developer FEV unveils a unique new engine design at the 2005 Society of Automotive Engineers World Congress.

DETROIT - FEV Engine Technology displays at the annual Society of Automotive Engineers World Congress here an intriguing opposed-cylinder diesel engine that leverages improvements to the 2-stroke cycle to generate thermal efficiency in excess of 41%.

The Opposed Piston-Opposed Cylinder (OPOC) design, says an FEV source, also generates extraordinary power density. A turbocharged 2-cyl. prototype on display generates 325 hp and 590 lb.-ft. (800 Nm) of torque at 2,000 rpm, yet weighs just 270 lbs. (123 kg).

Using a unique system of inner and outer connecting rods and cleverly positioned intake and exhaust ports, the OPOC design runs pistons in each opposed cylinder. The design causes the pistons to clamp together to develop compression and drive apart from the resulting combustion.

FEV says the inspiration for the OPOC design comes from both the Junkers Jumo twin-crankshaft diesel aircraft engine and the opposed-cylinder (“boxer”) design of Ferdinand Porsche.

FEV says the design, in eliminating cylinder heads and all valvetrain, has 25% fewer components, presenting the potential to dramatically reduce manufacturing cost and servicing complexity.

At the same time, the improvements to the 2-stroke cycle - focused largely on asymmetrically located intake and exhaust ports and a high degree of turbo boost - generates twice the power density of a typical poppet-valve 4-stroke engine.

The OPOC engine development program, conducted in conjunction with Advanced Propulsion Technologies Inc. (APT), was sponsored by the Defense Advanced Research Projects Agency as a potential power generator for military applications. (See related story: Military Humvees on Hybrid Trail)

FEV says the prototype engine has “almost no main bearing forces and very low piston side forces,” which significantly reduces operating friction. The prototype's four long connecting rods are constructed from titanium.

The engine also employs an electrically assisted turbocharger (EAT) developed by APT. An FEV source says the EAT is integral to the OPOC engine's ability to achieve the most from the 2-stroke combustion process.

The turbocharger's electrically assisted turbine can develop high levels of boost at low engine speeds that normally leave conventional turbochargers lacking. The FEV source says the EAT also can be used to precisely tailor the engine's torque output.”



The following, also for the OPOC engine of EcoMotors, is from http://www.hybridcars.com/bill-gates-in ... ine-28242/


“EcoMotors promises that the Opoc engine will provide a 50 percent fuel efficiency improvement on current engines while using half as many parts, and delivering a modular engine architecture capable of dramatically reducing emissions especially in city driving.

Gates (i.e. “the” Bill Gates of Microsoft), who invested through the Bill & Melinda Gates Foundation, said, “The Opoc engine can be an important step in providing affordable, low-emission transportation for the developing world.”



Reasonably, Bill Gates cannot be proud, today, for what he said then about the “promising” Opoc engine, nor for investing and loosing 23.5 US million dollars in EcoMotors OPOC.


I wonder why, neither FEV, nor Bill Gates of Microsoft, paid the US100$, or so, annual fee to keep the web site of EcoMotors active.




So I have to insist on:

There are deeper (technical) reasons for a good idea to not flourish (especially when it is supported by the biggest companies and richest investors).


Thanks
Manolis Pattakos

[J.A.W.]

Hi Manolis,
I can categorically state that Honda deliberately chose to cease retail sale of 2T motorcycles..
..& as an ideological policy, def' - not because of technical issues..

Case in point, per that EXP-2.. Honda sold an excellent variant of it as the 'CRM' 250 road-legal enduro bike,
& similarly they were still making money selling 2T 'CR' MX bikes, ( as Yamaha, in fact - still does) but ceased offering
them, insisting they were - per their beloved founder Soichiro Honda - 'in spirit', an 'all 4T company'..

Ironically, they still support their 2T range with parts manufacture & a US company buys their 2T MX engines &
transplants them into current model Honda MX chassis..

& as I have previously noted, a good selling item is missing from their range of out-door power tools, the chainsaw..
..even Honda knows it cannot compete in that department, a professional use 4T chainsaw would have to be built
from Ti/Mg, be turbo-charged, dry-sumped &... cost prohibitive..

As for 4T oil use, my Mercedes-Benz car seldom needs a top-up between oil changes, but it demands 7.5 lt of
top quality oil ( def' not ex-used & re-refined oil), & an expensive filter for each change too.. cost-wise its no
saving over a 2T - which uses only fresh oil & like quantity - over a similar running distance, sans filter & changes
- with disposal of waste hassles..

@ Pinger;
Re: your KTM 500, that'd be a goer, I had a KTM 380 EXC road-capable enduro, which was a good machine, but it was
mainly off-road focussed & seemed wasteful to use as a mere commuter, so while I had fun with it on a mate's farm,
I eventually sold it to him, since I wasn't using it enough..

KTM ought to sell a road bike version of their new Euro-4 emissions compliant EFI 300 2T, set in their light Duke chassis..
I'm sure their would be a market for it, & once established they could extend the range to a 600 twin & 900 triple..
I 'd buy a 150kg 150hp 2T 900/3..

& while on the subject of threes, Evinrude V6 outboards do utilize the inherent blowdown overlap of the 120`sequence.

[manolis]

Hello J.A.W.

You write:

“I can categorically state that Honda deliberately chose to cease retail sale of 2T motorcycles..
..& as an ideological policy, def' - not because of technical issues..

Case in point, per that EXP-2.. Honda sold an excellent variant of it as the 'CRM' 250 road-legal enduro bike,
& similarly they were still making money selling 2T 'CR' MX bikes, ( as Yamaha, in fact - still does) but ceased offering
them, insisting they were - per their beloved founder Soichiro Honda - 'in spirit', an 'all 4T company'..”



It doesn’t fit.


I can not say it “categorimatically”,

however,

did you ever think the case they use the “marketing policy” and the 4-stroke “heritage” of Soichiro Honda:



to hide the real issues / technical problems?

Thanks
Manolis Pattakos

[Pinger]

The common sense says: for some technical reasons and not for marketing reasons.

The EXP differed in it's method of initiating ignition at low loads. Nothing more. The architecture was as proven as can be. Simply no scope for technical difficulty.

At the same time, the improvements to the 2-stroke cycle - focused largely on asymmetrically located intake and exhaust ports and a high degree of turbo boost - generates twice the power density of a typical poppet-valve 4-stroke engine.

Just how much genuine time (ex ports closed, scavenge ports open) was there for supercharge? Without that a decent degree of supercharge is not possible without employing massive delivery pressure - which has its own cost. If the time was available - then how did they circumvent the torsional vibration problems that afflicted all other opposed piston designs employing large exhaust lead?

I wonder why, neither FEV, nor Bill Gates of Microsoft, paid the US100$, or so, annual fee to keep the web site of EcoMotors active.

Firms investing in losers as a tax avoidance ruse isn't new. Not saying that's the case here. Also, to be successful requires selling. Which requires buyers. If buyers can't be convinced to buy then it falls flat. Ask, why no buyers?

There are deeper (technical) reasons for a good idea to not flourish (especially when it is supported by the biggest companies and richest investors).

If there are technical reasons against it - then it isn't a good idea.

[Pinger]

@ Pinger;
Re: your KTM 500, that'd be a goer,

There's an Aprilia RS125 chassis here for it - the original plan...

& while on the subject of threes, Evinrude V6 outboards do utilize the inherent blowdown overlap of the 120`sequence.

I don't think the cross-charging concept using compact manifolding is as recognised as the effective technique it is. OBs make good use of it even though for space considerations they don't exploit it as fully as they could.
Doing all the calculations, one thing that struck me is that the longer the pipe lengths (eg expansion chambers) the more they suffer from being effective only over a narrow rpm range. Short, as per cross-charging, the effective speed range is almost the engines full rpm range.

[J.A.W.]

Hi Manolis,
Honda is a big company, & makes many engines, some of which are duds, like their super-costly 4T attempt to win..
.. their 1st FIM 500cc road-racing World Championship, against the long dominant 2T - the NR 500..
..but Honda did win it in 1983 with a 2T triple, with tech derived from their MX bikes, which had been 2T for a decade..

Honda was so proud of their victory at last, that they built & sold a 2T triple road bike, the MVX 250F.. alas - it was a dud..

See here: http://www.mcnews.com.au/honda-mvx250f-with-phil-hall/

Now Manolis, every dud Honda has built & gone public with, be in racing, or sold for everyday use, has such a webpage..

The EXP-2, & CRM 250, are definitively - not in that category.. Honda pissed off its 2T fans no-end, when they stopped..

& Pinger, I think you put too much unwarranted concern into 2T exhaust pipe tech as a cause of 'peaky' power..
Here below is a dyno chart of Yamaha's venerable 2T twin from the mid `80s, with rotary-drum exhaust valves.
The `86 model received an up-tune that gave a signifant power-boost over the `85, but still was not 'peaky'..

[Pinger]

& Pinger, I think you put too much unwarranted concern into 2T exhaust pipe tech as a cause of 'peaky' power..
Here below is a dyno chart of Yamaha's venerable 2T twin from the mid `80s, with rotary-drum exhaust valves.
The `86 model received an up-tune that gave a signifant power-boost over the `85, but still was not 'peaky'..

http://www.rd350lc.net/Magazine/MCI0986-5.jpg

Valves which control exhaust port height make all the difference - and on that basis I agree with you fully.
However, if you had driven my Villiers engined kart (I played with as a kid) or my Mk1 RG250 (which I still have - and a Mk2 YammaGamma - engine missing bits) you would agree with me! Maybe the Mk1 RG isn't standard (drilled gearbox drain plug - what else?) but peaky just does not describe its temperament. My mates RGV250? Oh so civilised by comparison - a lovely bike.

edit PS.
I forgot - I have ridden larger than 250. A 350RDLC. As you imply, very docile but still with that top end urge.

[manolis]

Hello Pinger.

You write:
“Manolis wrote:
At the same time, the improvements to the 2-stroke cycle - focused largely on asymmetrically located intake and exhaust ports and a high degree of turbo boost - generates twice the power density of a typical poppet-valve 4-stroke engine.”


No.
FEV and WardsAuto.com wrote this.




You also write:
“Just how much genuine time (ex ports closed, scavenge ports open) was there for supercharge? Without that a decent degree of supercharge is not possible without employing massive delivery pressure - which has its own cost. If the time was available - then how did they circumvent the torsional vibration problems that afflicted all other opposed piston designs employing large exhaust lead?”


Have you seen the PatATi? (at http://www.pattakon.com/pattakonPatAT.htm )

It can be Opposed-Piston Loop-Scavenged with asymmetric transfer and crankcase scavenging:



or Opposed-Piston turbocharged (or supercharged by an external air compressor) with Loop-Scavenged and 4-stroke-like lubrication:



In both cases the phase difference of the two crankshafts is zero (perfectly rid of free inertia forces and moments, perfectly rid of free inertia and combustion torques, too, in case it drives a symmetrical load (like, say, two counter[rotating propellers or two counter-rotating electric generators).


However even without being an Opposed Piston, the PatATi offers heavily asymmetrical transfer, either with conventional crankcase scavenging:



or with external scavenging:





The last animation shows a turbo-Diesel (say, for small airplanes) having “four-stroke-lubrication” in the crankcase, having transfer that closes substantially after the exhaust, having also a torque fluctuation (inertia and combustion) lower than the best V8 4-strokes.

Thanks
Manolis Pattakos

[Pinger]

Manolis:
The question I asked related to the degree of supercharge attainable (with opp piston) without running into torsional issues which historically (if Ricardo and others are to be believed) bedevil opp piston motors running high lead on the exhaust piston. Supercharging 2T isn't really viable without first closing the exhaust port substantially before the transfer ports.
Asymmetric transfer opening doesn't achieve this and your method in any case is more complicated than necessary.

But, the potential markets are what matters. Few have planes. Some have sleds (geography is all). More have boats (esp of the type that employ OBs). Even more have a motorcycle or scooter. Just about everyone in the developed world have cars and trucks are plentiful.
The proposed engine architecture has to suit these applications to gain acceptance and commercial success. There may be niche markets not described above but it will be a long slog to get everyone commuting to work by personal flyer. Arguably the most potential lies in the heavier engines (ships, trains, etc) but the capital costs there and the resistance to the 'new' make that very difficult markets to break into.
The most potential lies in the auto market, especially range extenders of electrified vehicles (IMO). Packaging in cars is everything. The engine architecture must be suitable. That it doesn't deviate overly from the known and accepted will be a bonus.
The one other application I have overlooked is hand held tools. But given advances in electrification there (the public's first preference - try sell them a 2T powered refrigerator!) it would have to be something pretty damned good to make a dent there.
In short, no sale without a market. The market defines the product - not the designer.

[manolis]

Hello Pinger.

You write:
“The question I asked related to the degree of supercharge attainable (with opp piston) without running into torsional issues which historically (if Ricardo and others are to be believed) bedevil opp piston motors running high lead on the exhaust piston.”

The Junkers Jumo 205:



has six cylinders and twelve pistons.

As shown at bottom-left, the crankpins of each crankshaft are equally distributed per 60 degrees; they shown at 0, 120, 240, 180, 300 and 60 degrees.

With the balance.exe program at http://www.pattakon.com/pattakonEduc.htm the free inertia torque is calculated at zero.

So, from this point of view, the arrangement seems perfect.


However, when the phase difference between the two crankshafts is wide, there are “torsional issues”.
The larger the phase difference, the worse the torsional issues.

How?

The total combustion torque in an Opposed Piston like the above Junkers Jumo, is the sum of the combustion torque acting separately on each one of its two synchronized crankshafts.
When the two opposed pistons of a cylinder are at their closest to-each-other position (i.e. when the combustion chamber volume gets minimum) the crankpin driving (through a connecting rod) the one piston is substantially before its respective “TDC” (which causes a heavy “negative” torque on its crankshaft), while the crankpin driving the other piston of the cylinder is substantially after its respective “TDC” (which causes a heavy “positive” torque on its crankshaft).
The instant total torgue (due to the combustion pressure) provided by the cylinder is the sum of the above two torques.
Increasing more and more the phase difference between the two crankshafts, the peak instant torque acting on each crankshaft separately, gets substantially bigger than the peak instant total torque provided by the engine.
This way the crankshafts (and the synchronizing gear between them) are overstressed (torsional issues).




You also write:
“Supercharging 2T isn't really viable without first closing the exhaust port substantially before the transfer ports.”


Not necessarily.

Suppose the transfer closes the same moment with the exhaust.
A turbocharger can still operate well / efficiently.

For instance, the moment the transfer and the exhaust ports close, the pressure in the cylinder can be, say, 2bar.

The idea is to prevent the exhaust from remaining open substantially after the transfer (as happens in the conventional 2-strokes), because this gives the chance to a good part of the fresh charge in the cylinder to escape to the exhaust.

And because the exhaust “needs” to open early (to give time for the pressure to fall before the opening of the transfer), a turbocharged / supercharged 2-stroke needs asymmetric timing.




You also write:

“Supercharging 2T isn't really viable without first closing the exhaust port substantially before the transfer ports
Asymmetric transfer opening doesn't achieve this and your method in any case is more complicated than necessary.”


Think of it again.


Because this is one of the things the PatATi can do: to close the exhaust port substantially before the transfer ports:





See the timing of the above model-engine; some transfer ports remain open for 15 crank degrees after the exhaust port is closed




The following “green” version:



not only closes the exhaust before the transfer, but it can also open the transfer only after the closing of the exhaust:





Think also again about the “complication” added by the PatATi method.

The working parts are only three:
the crankshaft,
the connecting rod
and the piston,

i.e. as much as in the simplest conventional 2-stroke (and fewer than in the good conventional 2-strokes because a PatATi needs neither reed valves, nor rotary valves).

The parts are shaped to perform additional tasks.

The asymmetric intake in a modern 2-stroke requires either a disk rotary valve in the crankcase, or a reed valve.
The PatATi offers as asymmetric intake as desirable without a rotary valve and without a reed valve. The cooperation of the piston with the connecting rod and the cylinder achieves this. And this is the opposite of “complication”.


Similarly for the asymmetric transfer:

In order to achieve asymmetrical transfer, Piero Baldini who “spent all his career designing two-stroke engines for Piaggio”, has invented / patented his Primavis engine:





Now take another look at the 800cc PatATi 2-stroke prototype engine we have made:





https://www.youtube.com/watch?v=aXvRaVqiHxs


Among others:

It is loop scavenged that allows a very compact combustion champer,

the exhaust can close before (even substantially before) the transfer without loading the "synchronizing gearing" (which is nothing more than a timing belt that runs unloaded),

the balance is perfect, etc, etc.


Thanks
Manolis Pattakos

[Pinger]

Manolis:

Perfect balance is laudable but not absolutely the last word. For example, in a RE application with the generator in unit there is no output torque force to resolve. Thus, the mountings to the chassis can be a soft as desired to isolate vibration without causing the usual difficulty encountered in a normal application.

Torsional issues with opp piston: Fair enough, if you want to dismiss Ricardo's findings. I don't. Neither do I understand exactly how they arise. Because opp piston architecture is of no interest to me for what I am pursuing, spending my time studying it detracts from my objectives. So I don't. But I don't casually dismiss the previous work of people such as Ricardo.

Supercharging (charging the cylinder to a pressure higher than prevailing ambient pressure) is not possible without adequate filling time after exhaust port closure. The more conventional architecture of single piston (as per your design and Primavis) when arranged to have the transfer port open long after exhaust closure exposes the transfer port to high pressure and temperature before and during blowdown. Hence Primavis making provision for extensive cooling in the valve area of its design. That complication and the additional complication of a more highly pressurised air supply (and with the extra air work) make any gains dubious against the additional complexities.

It all depends on the final application as envisaged (especially the aspect of whether the market will tolerate the additional costs incurred) but for me, as I have intimated previously, my interest lies in the simplest design that liberates a useful advance on what currently exists. For that reason I avoid untested sealing arrangements that will encounter higher than normal pressure and temperature. You, of course, are free to pursue your own path.

To illustrate my perspective further, The more complications we add to the 2T the further we take it from it's original virtues. And the more we do that, the greater is the tendency for industry to stick with the 4T. After all, if complexity becomes unavoidable, then the tendency will always be to stick to the known - the 4T. Which is pretty much where we find ourselves at this point in history.

[manolis]

Hello J.A.W.


Here is the arrangement of the Honda MVX250F (from your link):



The small end of the central connecting rod has to weigh as much as the small end of a side connecting rod plus a piston with its wrist pin and rings:




Quote from the above link:

“But it also became a weak point for the whole engine and real-time usage of the bike saw catastrophic failures of the conrod in the vertical cylinder.”


The “inertia” thrust load between the central piston skirt and its cylinder liner doubles.
Worse even, the inertia load on the big end bearing of the central cylinder doubles, too.


On the other hand, and despite the failures, Honda took the risk to play with unconventional solutions (motoGP V-5, NSR (oval pistons), EXP-2 (radical combustion), V-TEC etc), and this is good.

Thanks
Manolis Pattakos

[J.A.W.]

To illustrate my perspective further, The more complications we add to the 2T the further we take it from it's original virtues. And the more we do that, the greater is the tendency for industry to stick with the 4T. After all, if complexity becomes unavoidable, then the tendency will always be to stick to the known - the 4T. Which is pretty much where we find ourselves at this point in history.

Hi P, I think you dismiss the fundamental.. a power-stroke on every piston down-stroke - is the elephant in the room..

& 4T designs have being inexorably been steadily/incrementally becoming more complex/complicated over time,
but no one seriously suggests that the early/basic 4T ambient-atmospheric automatic inlet valve was/is - good enough..

& many 2Ts utilize turbo-charging, from aftermarket - high performance snowmobile kits, through Detroit Diesel mills,
to the WW 2 Junkers opposed piston, the Napier Deltic & Nomad, & the huge ship power plants used today..

Hi Manolis, the 2T engineering guys at Honda must have felt gutted, by the decision to cease series 2T production,
- but as you know - via Honda's published research papers & patent particulars, they haven't given them away completely..

[Pinger]

Hi P, I think you dismiss the fundamental.. a power-stroke on every piston down-stroke - is the elephant in the room..

Not at all! It is those stuck on 4ts who are blind to it. For the same output, cylinder pressures can be halved - and with it, much of the NOx issues vanish. Weaning them from their 4T habit is the challenge!

& 4T designs have being inexorably been steadily/incrementally becoming more complex/complicated over time,
but no one seriously suggests that the early/basic 4T ambient-atmospheric automatic inlet valve was/is - good enough.

.

I fully agree and the degree of complication in 4T is now ridiculous - and still no solution to NOx for diesel (that isn't an expensive addition which, the consumer has to pay for both initially and in the inconvenience of AdBlue top-ups which VW were obviously keen to negate by tuning down its operation once out of the testing lab).

That said, check the real world figures of (say) small Fiats available with both the expensive TwinAir and the older much simpler 2V/cyl 4 cylinder engine. There's not much in it re fuel economy and emissions. The cost of TwinAir gets harder to justify. Here in the UK the low depreciation of the simpler model is reflected in just how cheaply they can be leased (PCP etc where the depreciation only is paid by the lease holder). The downsizing revolution has stalled. See March 2017 (online) edition of Engine Technology International Magazine for more info.
As a snapshot of where we will be soonish, the TJI as discussed by Muniix appears to be the engine which will replace diesel. However, if reliant on EGR etc, it will still be a relatively expensive engine to build. A simpler 2T for say, RE may well be in demand also.

& many 2Ts utilize turbo-charging, from aftermarket - high performance snowmobile kits, through Detroit Diesel mills,
to the WW 2 Junkers opposed piston, the Napier Deltic & Nomad, & the huge ship power plants used today...

For scavenging yes. The degree of supercharge is debatable, dependent on the lead of exhausting. Higher level of air work and higher levels of NOx again count against supercharging.


That small end on the Honda V3 is horrible. Are you still happy to add weight to the upper end of a con rod Manolis?

[J.A.W.]

...For scavenging yes. The degree of supercharge is debatable, dependent on the lead of exhausting. Higher level of air work and higher levels of NOx again count against supercharging.

Ah, no.. P, those machines all had the scavenging process already sorted out, the turbocharger was additional, either to
maintain ambient pressure over an altitude gradient, or for lower levels, such as at sea-level.. purely for ++ power..
..& efficiency, in utilizing the energy of copious exhaust pulses..