jeforton

iTrader: (3)

so with the gen 5's being direct injection, and having some experience with diesels, a thought occurred to me: why not tune it to run like a duramax? up compression to say 16:1 and put a turbo or two on. tune spark timing out late enough to not matter, adjust the injection tables to handle combustion events. without fuel in the air at compression it won't knock, so you could run big boost ie 50+ psi. if a 6.6L duramax can make 800rwhp on straight fuel at 3000 rpm... makes me wonder what an LT1 could do at 6500 rpm with the same principal. has anyone else thought of this? could the injection tables even be tweaked enough to make this possible?

redtan

iTrader: (5)

It takes alot more than just direct injection for you to run 50psi on a 16:1 compression gas engine.

Wnts2Go10O

iTrader: (12)

uhh.. arent diesel internals built to take the loads that 16:1 compression and a **** ton of boost put on them? not to mention the fuels ability to resist detonation, etc?..

jeforton

iTrader: (3)

let's pretend this engine has all required support mods, head studs, forged internals, fire rings, etc.

maybe i worded it wrong. i'm not asking if an LT1 can take 50 pounds of boost. diesels make great power partly due to the fact that they can't pre-detonate. you can pump a large amount of air in, and add fuel only when you're ready for ignition. that's why you see diesels with massive turbo systems. the same principal applies here. what's been limiting the power output of the lsx engines? most people want to run pump gas. so they can only get cylinder pressures so high before it detonates. with direct injection you don't have that problem. so instead of stopping at 18-20 psi (what ever the case may be) because you don't want to run race fuel, you can still run 93 from the pump and keep upping the boost pressure. so point being, i foresee much larger induction systems on these engines than we have seen in the past.

i don't know what the injection timing vs spark timing looks like on this engine, but i'd assume the injectors fire a fair bit sooner than the spark plugs. so as boost comes up, cylinder pressure goes up and you run the risk of detonating before the spark. that's why i suggested retarding the spark and injection until the injection happens where you want ignition. that's also why i suggested bumping compression to force the detonation in a predictable manor, like diesels do.

as for diesel fuel resisting detonation, no. it lights up nearly instantly after injection. it essentially turns the injector into a mini flame thrower if the pulse width gets too long.

and for strength, lb7 (01-04 duramax) the stock connecting rods tend to bend much after 600rwhp. the internals aren't made of adamantium, they're just bigger than what you'd find in an ls1.

dirty_old_chevy

I've always wondered about this way of thinking too. Not to these extremes, but all the same. You cant have pre-ignition if there is no fuel in the combustion chamber before TDC. I suppose you could have detonation/irradic burn when the piston is on the downstroke. If you had a water injection system, this would help cool the piston and combustion chamber before the powerstroke.

Wnts2Go10O

iTrader: (12)

ah. you want to use the philosophy of injection immediately before ignition. it working depends on how the flame front propagates and how quickly between the 2 fuels. you also have to take atomization into consideration among a few other things. the question is.. would you be able to inject all the fuel you need at ~7k rpm then ignite immediately after fast enough? or would this be mostly for 0-~3,000 rpm?

jeforton

iTrader: (3)

gasoline burns faster than diesel does. that's partly why you don't see diesels turning rpm like gas engines. much over 6000 rpm it can't burn fast enough for a complete burn before the exhaust valve opens. at that point you'd be seeing smoke even if you aren't running rich. as for injecting fast enough, you'd just need big enough injectors to keep pulse width short at higher rpms and a fuel pump capable of keeping pressure in the rails. as for ensuring instant ignition that's why i figured on bumping compression. make sure the air charge is hot enough to light the fuel as soon as it hits.

Bring the Noise

Gas doesn't burn it explodes (then the multi ignition spark systems burn off a decent amount of the remaining fuel).

Diesel on the other hand Burns and does not explode (that is why they have glow plugs and not Spark plugs).

Diesel makes power from the rapid expansion of the burn/smoke in the chamber. This is why they use a higher compression and a higher injector pressure to feed the flame (so yes it is a flame thrower in a controlled environment).

Gas engines rely on the fuel to atomize into the air so that when a spark is ignited the compressed air/fuel mix will explode, not burn. To high a compression and the fuel can ignite without a spark (aka premature detonation or knock).

Completely different ideas, and you could probably turn a LT1 into a diesel to do what you want.... but the aluminum heads and block may not handle the pressures for an extended period of time (in other words it may not make it for 100,000 miles as a diesel).

But then again what do I know, I've only been tinkering with motors for 30 years off an on....

wssix99

iTrader: (5)

I think you hit on the point that the direct injection technology has matured in Diesels and has come to Otto engines. As pointed out above, an Otto engine is not typically built to handle the pressures generated in the Diesel cycle.

Interestingly, there has been some recent research in to Hybrid Cycle engines. You might start here and find some interesting reading: http://en.wikipedia.org/wiki/High-ef...y_hybrid_cycle

texas94z

SIDI engines can operate in stratified conditions like a diesel engine, injecting fuel during the compression stroke. However, there is no time for mixture formation at high engine speeds, therefore limiting performance. The Gen 5 LT1 only operates in stratified mode during light loads. This condition produces an ultra lean burn to maximize fuel efficiency.

jeforton

iTrader: (3)

when i read people talking about flame travel in the cylinder i figured gas burned rather than exploded. guess that does kind of put a damper on things.

i understand that a stock gas engine isn't designed to take the stress of a built diesel engine. i'm not talking about trying to make an all aluminum engine that makes 1500ft/lbs at 2000 rpm and continues making power up to 6000 rpm. just talking about trying to push the edge a little with an idea that might not have been explored before.

thanks for the link, i'll look into that.

texas94z

No bro, your basic conceptual ideas are very foreword thinking, but theory is just off a bit.

The combustion system you described may be the technology found in the next generation GM small block. Your concept is relatively similar to the combustion system called homogeneous charge compression ignition or HCCI. You may have ran across this technology before because it's been published that GM has worked extensively on this technology for many years.

In short, HCCI is basically a spark ignition engine that can operate like a diesel engine under certain variable conditions. Diesel performance in a gas engine. When in diesel mode, the ecu kills the spark ignition and creates a near perfect homogenous air/fuel mixture that auto-ignites at a specific time. Auto-ignition is caused by the heat and pressure caused by compression, a la diesel engine.

The advantages to this combustion system are significant. Most notably, efficiencies across the board are improved to diesel engine standards but without diesel-like emissions, a monumental gain for gas engines.

This is the most basic description of this upcoming combustion system. A HCCI GM small block is evident in the future, and the DI Gen 5 LT1 is proof of that transition.

Wnts2Go10O

iTrader: (12)

so black powder vs smokeless

so tex, i was basically correct on my questioning if it could 'keep up'?

wssix99

iTrader: (5)

Gas and Diesel both burn and explode.

Burning is the same thing as combustion and it describes the chemical reaction of oxidation. Both gas and diesel oxidize in the combustion chamber: http://dictionary.reference.com/browse/combustion

Exploding has to do with speed and the rapid increase of volume and pressure: http://dictionary.reference.com/browse/explosion?s=t Both gas and diesel explode (under different conditions) and both use this explosion to move the pistons.

It's hard to compare the burn of gas and diesel engines. In a gas engine, the flame front starts from the spark plug and expands outward. In an ideal diesel engine, (no help from the glow plug needed) the fuel/air mixture combusts in a diffuse manner all around the cylinder space once it reaches a critical pressure/heat.

I'm not a chemist or an expert on combustion, but I like this explanation for why Diesel engines can't get to the higher RPM ranges: (because a longer stroke is required) http://wiki.answers.com/Q/Is_a_diese...esel_burn_rate

spare tire

iTrader: (3)

So your saying diesel engines run off the glow plugs?
Glow plugs are only used for starting the engine, cummins ISB engines dont even have glow plugs just a grid heater.

Also here are some example of diesels that turn a decent amount of RPM (not like a gas engine can though.) From what i understand the mfg. limit the rpm they turn for durability/ wear.
Im sure an engine that is limited to 3000rpm is gonna outlast an engine that turns 6500rpm.
http://www.dieselpowermag.com/featur...l_race_trucks/

wssix99

iTrader: (5)

No. I said an ideal diesel running at its steady state doesn't need them.

spare tire

iTrader: (3)

lol i didnt read your quote my bad. Makes sense now.

SNLPerformance

iTrader: (15)

An advancement of this?http://www.hotrod.com/techarticles/e..._vapor_engine/

texas94z

Smokey was a genius. Like the article said, he took much of his knowledge to the grave which is extremely disheartening. Smokey's hot vapor engine was incredibly power dense and efficient for its time, which is crazy without ecu accurately controlling fuel injection. I need to research more about his work and this engine in particular. However, I can tell you that there is a major draw back to his design. When auto manufacturers design an engine, engineers compromise between performance, fuel efficiency and emissions. Smokey completely ignored emission output when he design this engine. Due to the ultra lean and high temperature conditions, NOx formation skyrockets thus requiring emissions equipment that I'm sure the engine did not carry. That's possibly why we don't see this design on roads today. But, maybe with modern emissions equipment the design could be viable.

One thing is certain is that Smokey was a freakin' genius. His understanding of homogenous mixtures, flame fronts, lean burn conditions and the ICE in general was way of the time. Like a said, I need to conduct more research to grasp his theory.

cam

iTrader: (9)

All thats fine and dandy but anyone know for sure what the limits are on the stock injectors?