Asinine Engineering: Direct Exhaust Injection
Hang around internet fora dedicated to increasing internal combustion performance long enough and you'll eventually run across this type of perpetual-motion misunderstanding. Seems a Vette 'boarder over at the GMModernMuscle Forum needs to study up on several principles before heading out half-cooked, wrench in hand. The brilliant idea that dawned above the poster's head like a 3-watt bulb was that instead of messing around with those ever so inefficient turbochargers, it'd be a simpler route to just run the exhaust back into the intake manifold to put the intake tract under positive pressure. Reading through the multitudinous pages of fodder, this is either someone with "issues" or just a jokester troll.
If he is serious, let's lay out a few simple things here. Firstly, there's not very much oxygen in the exhaust gas, which would make recombustion rather difficult. Second, it's tremendously hot. Third, his assumption that a turbocharger is driven by high-pressure exhaust gas pulses is incorrect. What drives a turbocharger is the expansion of the exhaust gas as it cools and depressurizes. It's the same way an air conditioner works, and it's really thermodynamic theory when you get right down to it. Sure, the exhaust gas is under pressure, but if you think that a turbine is an inefficient way to compress air, pistons are only more so. There's a lot of mass to swing around, and the poppet valves in an automotive cylinder don't improve airflow versus what a compressor housing of a turbo can do, either. Before you raise the EGR flag, let's note that exhaust gas recirculation is used to control combustion pressure and temperature, and since it takes up space that would otherwise be occupied by oxygen-rich intake charge, it's a performance detriment. Finally, how is the engine going to breathe when you've basically set up an infinite feedback loop? We're sure that these sticky engineering challenges are all easily worked out on a bar napkin, though. Why have automakers been denying us the pleasure of this simple high performance option for so long? They must be in cahoots with turbo manufacturers, that's all there is to it.
Thanks for the tip, Richard
[Source:GMModernMuscle]!
Reader Comments (Page 1 of 4)
Nick 1:18AM (3/31/2008)
Maybe i'm f*cked in my thinkin here bro, but your turbo explanation isn't makin much sense, gas contracts as its cooled - steam rises.
Reply
Will 1:15PM (11/16/2007)
I saw this a couple weeks ago and read the forum. He's clearly joking, and I think it's hilarious that people who don't grasp that are flaming him for it.
Reply
bonejob 3:24PM (11/16/2007)
Is he really "obviously" joking? I don't think so. I've heard moronic ideas like this (and worse) from people who are dead serious and have gotten seriously pissed off when they see my face turning purple from hypoxia as I'm laughing my ass off.
Matt 3:36AM (11/17/2007)
This is a repost x eleventy billion. It first started popping up around 2001 if not earlier :/
Derek 6:43PM (11/16/2007)
Agreed, the people that get this are laughing their asses off at the people that are taking this guy serious. It doesn't take long to figure out that this guy has set up some other accounts on there, kinda like a one man show of hilarity.
If you've been on automotive boards for very long you'll this is nothing new, these have been around for a while.
Anyone remember having to take your car to Honda to get the VTEC update? Check your blinker fluid lately? How about parts for your 83 Covette? Water pump for a 67 Beetle ?
Ever buy parts from here?
http://kalecoauto.com/index.php?main_page=index
naggs 7:21PM (11/16/2007)
lmao, replacement wiring harness smoke
Russell 7:45PM (11/16/2007)
It looks like he's 5 years old, or just never developed further.
Derek 8:28PM (11/16/2007)
ha, I haven't heard that one before.
Also you can take bird droppings, tree sap, and road tar of your paint by soaking the area affected in brake fluid or non-Honda steering fluid! It's cheaper than clay baring it!
Frustrated Consumer 1:17PM (11/16/2007)
I think it's even weirder that someone thinks turbochargers and air conditioners are essentially the same thing...
Reply
bonejob 3:24PM (11/16/2007)
Yes, they DO have plenty in common. They both operate on the exchange of heat by means of compressed gases through the use of a compressor. In a turbo-charged engine, heat from the exhaust side is transferred to the intake side, causing a pressure increase due to expansion of the heated air in the intake manifold. As the intake air is heated, the exhaust is COOLED.
Turbos are especially efficient in diesel applications, because the hotter the intake air, the more complete the diesel combustion. In gasoline motors, this extra heat has to be carefully managed because too much heat in the intake air can cause detonation, which in extreme cases can literally blow holes in the piston crowns. This is not a concern in diesels because detonation is how diesels work; gasoline needs spark and slow burn, diesel is ignited through compression followed by a very fast burn (in other words, detonation), the faster the better.
In air conditioning, the same principle is used. Through expansion on the intake side and compression on the exhaust side, heat is transferred from one place (one's house or car interior) to another (the outside). The only real difference is that air conditioning compressors are driven by electric motors (or engines' crankshafts) and turbochargers are driven by expanding gases from the burning of fuel, usually (but not always) in an internal combustion engine.
Turbocharging is, in essence, a method of recovering and recycling heat that would otherwise be thrown away with the exhaust. Thermodynamicists call internal combustion engines "heat engines" for a reason. All "heat engines" are essentially heat pumps that are driven by the burning of fuel in a closed space. An engine just converts the potential energy in fuel into the kinetic energy needed to do work, in most cases, moving a vehicle. A turbo is just a means of achieving this more efficiently, with less heat wasted.
naggs 3:02PM (11/16/2007)
an air conditioner converts mechanical energy into a temperature differental and a turbo converts a temperature differential into mechanical energy
not the same thing persay but the both operate under the same principales
cowboy bob 9:07AM (11/17/2007)
Sayyy, bonejob. You seem to be quite well informed. Very good explination. Seriously. Now get out. You clearly don't belong here.
Alex 1:17PM (11/16/2007)
Dan - Clearly you are in bed with the turbo manufacturers too.
Reply
Fooman 1:21PM (11/16/2007)
If you read the whole thread, and follow up on the rep this guy has on the forums, unfortunately this guy is serious. Hard to believe but this guy is dead serious. He also thinks he has the oldest c4 vette outside a museum. He has also had a few other crackpot ideas, and could not keep a job at Walmart.
He feels that you are routing only half the exhaust back into the system and that if he "leans" out the mixture it will work.
It does make a kinda Darwin Award type of sense...
Reply
chrisdavis 1:22PM (11/16/2007)
"What drives a turbocharger is the expansion of the exhaust gas as it cools and depressurizes."
Is that his thinking or yours? It's far more entertaining if you're flaming him with this "logic" so I will assume you believe this to be true
Reply
mctaylor82 1:35PM (11/16/2007)
Agreed.
If Autoblog thinks that air expands as it cools and "depressurizes", then it's got a lot more to learn before it starts touting it's knowledge of basic thermodynamics.
PGAero 1:39PM (11/16/2007)
Agreed Chris. See my comment below.
~P
chrisdavis 1:43PM (11/16/2007)
Hey Autoblog, read up
http://auto.howstuffworks.com/turbo1.htm
naggs 3:46AM (12/03/2007)
im not sure why everyone is bashing Dan here.
as the exhaust gas does work (driving the turbo) it expands and cools.
am i missing something?
daInvincibleGama 4:22PM (11/16/2007)
Yes, you are missing something. Gases occupy less volume as they cool. Only warming up a gas would expand it. It's called Charles' Law.
What drives a turbocharger IS the hot, pressurized gas coming out of the combustion chamber. That gas cools down as it transfers its energy into the turbine rotation (heat becomes mechanical work), which then powers the forced induction. That is why turbochargers create a certain amount of exhaust backpressure, sometimes necessitating upgrades to exhaust valves/piping to extract the most performance.
LOL @ Autoblog for "correcting" his mistakes. Even though his idea was undoubtedly ridiculous, it was most likely a troll. Meanwhile, you managed to make a fool of yourself. I'm surprised there are only so many posts questioning your logic(?).