Search | Car Forums | Gallery | Articles | Helper | AF 350Z | IgorSushko.com | Corporate |
| Latest | 0 Rplys |
|
Car Comparisons Compare any cars and find out what every body else thinks. Just refrain from making stupid comparos like Viper vs. Geo Metro :) |
Show Printable Version | Email this Page | Subscribe to this Thread |
|
Thread Tools |
02-02-2004, 09:25 PM | #31 | ||
AF Enthusiast
|
Re: piston vs rotary engines!!??
Quote:
|
||
02-03-2004, 01:28 PM | #32 | |
The Red Baron
|
First, I'm not pissed. Second, the piston does have to fight the inertial forces on it and if you really want to delve into physics I suppose it does stop but for a nearly immeasurable amount of time.
Still, it is far more efficient than a rotary. |
|
02-03-2004, 03:33 PM | #33 | ||
AF Enthusiast
Join Date: Feb 2003
Posts: 690
Thanks: 0
Thanked 0 Times in 0 Posts
|
Re: piston vs rotary engines!!??
Quote:
Position is constantly changing, and the rate of change of position is constantly changing. Piston Velocity is zero at TDC and BDC, but the rate of change of piston velocity is constantly changing. The time the piston is stopped is 0, but there are two points where it is stopped. Piston acceleration is zero at the midpoint of the stroke (this is only true for constant RPM, with changing RPM the location of zero acceleration can move slightly), but the rate of change of the acceleration of the piston is constantly changing. The time the acceleration is stopped is 0, but there is a point where there is no acceleration. I hope that clarifies a few things. Efficiency of an internal combustion engine is higher than for a rotary engine. Exactly why this is the case is beyond my knowledge base, a good indicator of this is the HP:Fuel Mileage ratio. A normally aspirated gen II RX7 makes about 160 HP and gets about 20 MPG, where a Porsche 944 is about 150 HP and gets about 25 MPG. A gen III RX7 Turbo makes about 270 HP and gets about 18 MPG, and a Nissan 300ZX Twin Turbo makes about 290 HP and gets about 20 MPG. There are a lot of other factors involved, but generally the efficiency for an internal combustion engine is around 20-22% and is about 18-19% for a rotary. This is all based on memory, so the exact numbers could be off, but the general idea is the same. The problem with increasing boost in a rotary is the reliability of the apex seals. You do get a higher percentage gain in power and tourque for a rotary, but you can run more boost in a internal combustion engine more reliably than in a rotary.
__________________
2004 Subaru Impreza WRX STI (daily driver) 1999 Mazda Miata (track car, slow, but finished the SCCA Runoffs) 1987 Porsche 944 (being rebuilt) |
||
03-17-2011, 05:05 AM | #34 | |
AF Newbie
Join Date: Mar 2011
Location: Kalamazoo, Michigan
Posts: 1
Thanks: 0
Thanked 0 Times in 0 Posts
|
Re: piston vs rotary engines!!??
Acceleration on a piston in a piston driven engine is NEVER zero. While one cylinder might be at tdc or bdc, another one is in it's combustion stroke. Since all cylinders are attached to the same crankshaft, the combustion in one cylinder would add acceleration in another. And all the pistons would have gravity acting on them.
Also: Yes, velocity at the top of the piston reaches zero, but the bottom does not. Velocity is a measure of both speed and direction in a three dimensional space. At tdc and bdc, the crank may change direction vertically, but it is always moving around the crank, thus always has velocity. |
|
|
POST REPLY TO THIS THREAD |
Thread Tools | |
|
|