Re: Honda Civic SI Concept Information
 

"jim beam" <nospam@example.net> wrote in message
news:1113573749.1f231197caffc4bf617d6a3c649c1755@t eranews...
> Brian Smith wrote:
>> "Jason" <jason@nospam.com> wrote in message
>> news:jason-1404051015100001@pm4-broad-28.snlo.dialup.fix.net...
>> It's a common misconception that a lot of people have, that a bigger
>> engine means more fuel consumed.
> wow, that's an awesomely underinformed pair of statements. the
> fundamental fact is that bigger engines have more friction & more
> reciprocating mass, therefore they /do/ require more energy to run. 8
> cylinders take more energy to run than 4 cylinders for the same reasons.
> the "improvement" experienced between those two motors was entirely due to
> differences in ignition & fuel/air delivery technology, not some bizarre
> local distortion in the fundamental rules of physics.
>
Still, it is a fact of life. All things being equal, your statement is
certainly true. The problem is that there are a lot of variables -
compression ratio, gearing, throttle losses, etc. If every chassis were
tried with every available engine the most efficient would probably be one
of the smallest, but we would find a lot of bumps in the graph of economy as
a function of power or displacement. For example, the EPA MPG ratings
(http://www.fueleconomy.gov/feg/FEG20...neVehicles.pdf) for the BMW Z4
roadster 6 speed 3.0L is better than for the 5 speed 2.5L. Probably the
improved gearing doing that, but there we are.

In theory, gasoline engines (otto cycle) have a thermodynamic limit of
efficiency around 65% while diesel engines (diesel cycle) have a limit of
efficiency around 50%. But since those limits are approached as the
compression ratio approaches infinity, the diesel wins almost every time.

Mike

Re: Honda Civic SI Concept Information
 

When grilled further on (Fri, 15 Apr 2005 12:27:29 -0700),
"Michael Pardee" <michaeltnull@cybertrails.com> confessed:

>
> In theory, gasoline engines (otto cycle) have a thermodynamic limit of
> efficiency around 65% while diesel engines (diesel cycle) have a limit of
> efficiency around 50%. But since those limits are approached as the
> compression ratio approaches infinity, the diesel wins almost every time.

Why is it that gasoline engines cannot (will not?) achieve higher compression
like the diesel?

Thanks,
Rob

Re: Honda Civic SI Concept Information
 

When grilled further on (Fri, 15 Apr 2005 12:27:29 -0700),
"Michael Pardee" <michaeltnull@cybertrails.com> confessed:

>
> In theory, gasoline engines (otto cycle) have a thermodynamic limit of
> efficiency around 65% while diesel engines (diesel cycle) have a limit of
> efficiency around 50%. But since those limits are approached as the
> compression ratio approaches infinity, the diesel wins almost every time.

Why is it that gasoline engines cannot (will not?) achieve higher compression
like the diesel?

Thanks,
Rob

Re: Honda Civic SI Concept Information
 

----- Original Message -----
From: "Rob" <anonlcNOSPAM@gmail.com>
Newsgroups: alt.autos.honda
Sent: Friday, April 15, 2005 8:23 PM
Subject: Re: Honda Civic SI Concept Information


> When grilled further on (Fri, 15 Apr 2005 12:27:29 -0700),
> "Michael Pardee" <michaeltnull@cybertrails.com> confessed:
>
>>
>> In theory, gasoline engines (otto cycle) have a thermodynamic limit of
>> efficiency around 65% while diesel engines (diesel cycle) have a limit of
>> efficiency around 50%. But since those limits are approached as the
>> compression ratio approaches infinity, the diesel wins almost every time.
>
> Why is it that gasoline engines cannot (will not?) achieve higher
> compression
> like the diesel?
>
> Thanks,
> Rob
>
Detonation (self-ignition) is the problem there. It isn't an issue in the
diesel cycle because the fuel isn't introduced until the compression has
heated the air charge to the ignition point.

That difference also accounts for the difference in theoretical limit of
efficiency. The otto cycle adds heat at constant volume (less true at higher
rpms than lower rpms, naturally), while the diesel cycle is deemed to add
heat at constant pressure.

Mike

Re: Honda Civic SI Concept Information
 

----- Original Message -----
From: "Rob" <anonlcNOSPAM@gmail.com>
Newsgroups: alt.autos.honda
Sent: Friday, April 15, 2005 8:23 PM
Subject: Re: Honda Civic SI Concept Information


> When grilled further on (Fri, 15 Apr 2005 12:27:29 -0700),
> "Michael Pardee" <michaeltnull@cybertrails.com> confessed:
>
>>
>> In theory, gasoline engines (otto cycle) have a thermodynamic limit of
>> efficiency around 65% while diesel engines (diesel cycle) have a limit of
>> efficiency around 50%. But since those limits are approached as the
>> compression ratio approaches infinity, the diesel wins almost every time.
>
> Why is it that gasoline engines cannot (will not?) achieve higher
> compression
> like the diesel?
>
> Thanks,
> Rob
>
Detonation (self-ignition) is the problem there. It isn't an issue in the
diesel cycle because the fuel isn't introduced until the compression has
heated the air charge to the ignition point.

That difference also accounts for the difference in theoretical limit of
efficiency. The otto cycle adds heat at constant volume (less true at higher
rpms than lower rpms, naturally), while the diesel cycle is deemed to add
heat at constant pressure.

Mike