Diesel engines- forced induction, power-weight

[Jay]

From what I understand, the low power to weight ratio of diesel
engines has been the main limiting factor for their adoption into
small planes (and passenger cars for that matter). The reason for the
high weight as it was explained to me was that the high compression
used for an auto-ignition type engine required strong, and thus heavy
castings to withstand the pressures.

So these days you see diesels fitted with forced induction systems,
which apparently makes them more peppy (e.g. the 90hp VW 1.9L TDI).
But doesn't this more powerful charge being introduced by the forced
induction system, just require again, a heavier engine to withstand
the more powerful explosion? Or to put in in converse, if the same
engine could have withstood the more powerful charge, couldn't they
have built it lighter in the first place and used a conventional
induction system? For now lets ignore the altitude power
normalization aspect for aircraft operation.

[Ed Wischmeyer]

> So these days you see diesels fitted with forced induction systems,
> which apparently makes them more peppy (e.g. the 90hp VW 1.9L TDI).

Check out the RPMs at which the various diesel engines develop their
power (I don't have any numbers in front of me, so I'll let you do the
web search). That's part of the answer.

Ed Wischmeyer

[Ernest Christley]

Jay wrote:
> From what I understand, the low power to weight ratio of diesel
> engines has been the main limiting factor for their adoption into
> small planes (and passenger cars for that matter). The reason for the
> high weight as it was explained to me was that the high compression
> used for an auto-ignition type engine required strong, and thus heavy
> castings to withstand the pressures.
>
> So these days you see diesels fitted with forced induction systems,
> which apparently makes them more peppy (e.g. the 90hp VW 1.9L TDI).
> But doesn't this more powerful charge being introduced by the forced
> induction system, just require again, a heavier engine to withstand
> the more powerful explosion? Or to put in in converse, if the same
> engine could have withstood the more powerful charge, couldn't they
> have built it lighter in the first place and used a conventional
> induction system? For now lets ignore the altitude power
> normalization aspect for aircraft operation.

Having spent years behind the big wheels, power to weight is probably on
the bottom of my list for not having a diesel in a small vehicle of any
type.

Your burning kerosene there, so the pistons have to take their time to
give those long carbon chains time to burn down. The engines I sat on
top of usually ran between 1800 and 2100 RPM, were slow to rev up, and
shook like a crack whore. Anything that shook like that would tear an
airplane apart, and would be very uncomfortable in a passenger car.

--
http://www.ernest.isa-geek.org/
"Ignorance is mankinds normal state,
alleviated by information and experience."
Veeduber

[Dan Brown]

Ernest Christley > wrote in news:TLtAb.79227
:

> Having spent years behind the big wheels, power to weight is probably on
> the bottom of my list for not having a diesel in a small vehicle of any
> type.

We're getting way off-topic for this group, but if you're at all
interested, test-drive a VW (Golf, Jetta, Bettle) TDI some time. Not
rockets by any means, but they're reasonably peppy. At idle, you can tell
it's a diesel, but when it's moving, it's quieter than the gas engine (due
to lower revs). I'd think it's a bad candidate for aircraft use because of
power/weight, but it's great for a car (which is why I drive one).

[R. Hubbell]

On 6 Dec 2003 09:32:52 -0800 (Jay) wrote:

> From what I understand, the low power to weight ratio of diesel
> engines has been the main limiting factor for their adoption into
> small planes (and passenger cars for that matter). The reason for the
> high weight as it was explained to me was that the high compression
> used for an auto-ignition type engine required strong, and thus heavy
> castings to withstand the pressures.


Times have changed and materials science has taken some huge leaps. Modern
diesels are cleaner and quieter then just 10 years ago.

>
> So these days you see diesels fitted with forced induction systems,


I didn't think forced induction was anything new to diesel engines.

> which apparently makes them more peppy (e.g. the 90hp VW 1.9L TDI).

It definitely makes them peppier and more efficient.


> But doesn't this more powerful charge being introduced by the forced
> induction system, just require again, a heavier engine to withstand
> the more powerful explosion? Or to put in in converse, if the same

Again, materials have advanced greatly and the parts can be made lighter
and stronger.


> engine could have withstood the more powerful charge, couldn't they
> have built it lighter in the first place and used a conventional
> induction system? For now lets ignore the altitude power


What do you mean by conventional induction system?


> normalization aspect for aircraft operation.


Don't ignore that, that's one of the best features. :)


R. Hubbell