Diesel Engine and fuel questions?

AndyRV7 · #1 10-26-2007, 01:14 PM

What is the value of a TD engine? I've seen a few posts here and there discussing that we need turbo engine choices. I don't see why. Cessna just (coincidentally) came out with a TD Skyhawk. It makes less power and performance than the same plane with a 100LL engine in it. So what is the advantage of this technology? Is diesel fuel even available everywhere? And does it mean that we can continue to fly without being squeezed out of the hobby by operational costs?

Thanks. Andy

RV6_flyer · #2 10-26-2007, 01:56 PM

I occasionally run waste Jet A in my TDI VW Beetle diesel. Jet A is available at many airports and will run in the diesel engines that are starting to become available for general aviation aircraft.

The Turbo helps the diesel make much more power than it does without the turbo. On my 1.9L VW diesel, the turbo make my little 90 HP engine feel a lot like the 150 HP 2L gas engine. Acceleration is almost as good as the gas powered engines. The diesel has a lot of torque. Without the turbo, the diesel car is a DOG and very slow getting out of its way. If I were to let you drive my diesel car and did not tell you it was a diesel before hand, you would not know it were a diesel.

Gasoline engines must have the correct ratio of fuel to air for the mixture to ignite. Diesels begin combustion from the heat of compression. Diesel will burn all of the fuel in an air rich environment. In a gasoline engine, we call that lean of peak. If you put in too much fuel and not enough air into a diesel, you get incomplete combustion and black smoke. If you use a turbo, you can add more fuel thus making more power.

A turbo on a diesel is a great way to add more power without decreasing reliability. My VW TDI is 9-years old, has over 230,000 miles, get 51 MPG at 58 mph on the highway, and only used about 1/4 a quart of oil in 3,200 miles. BTW, the compression ratio is 19.5:1. As for reliability, VW will be starting an ad campaign in 2008 to reintroduce their CLEAN AIR 50 state legal diesel car to the US market. The ad will feature an older VW diesel that was found in Ohio that still has its original engine with over 585,000 miles.

Typically a diesel engine is 30 to 40% more efficient than a gasoline engine. Read that to mean that it will use less fuel to make the same power.

Sorry if this is more car related but I like my 9-year old TDI as much as my 10-year old RV. Hope I did an adequate job with the diesel explanation.

John Clark · #3 10-26-2007, 03:02 PM

Quote:

Originally Posted by AndyRV7

What is the value of a TD engine? I've seen a few posts here and there discussing that we need turbo engine choices. I don't see why. Cessna just (coincidentally) came out with a TD Skyhawk. It makes less power and performance than the same plane with a 100LL engine in it. So what is the advantage of this technology? Is diesel fuel even available everywhere? And does it mean that we can continue to fly without being squeezed out of the hobby by operational costs?

Thanks. Andy

The availability of 100LL is in question long term for two reasons. First, it is less than 1% of the gasoline produced in the US and requires special handling and distribution. Second, it contains tetraethyl lead, a super toxic substance (Google it, you will be amazed.) The Diesel can run on Jet A. Jet A will be around because it is produced in much higher quanities. The diesel will get better "mileage" because there is more heat (calories) in a gallon of diesel than in a gallon of 100LL. There is a slight trade-out in that Jet A is a little heavier than 100LL. Roughly 6 lbs for 100LL vs 6.82 lbs for Jet A, depending on the temperature.

John Clark
RV8 N18U "Sunshine"
KSBA

AndyRV7 · #4 10-26-2007, 03:02 PM

That actually clears up some of the things I didn't understand. That is, why some people were using TD and Jet A in the same sentence. Also, why a TD engine might be a good option (purely from an efficiency standpoint).

Any opinion why Cessna would not put a larger displacement, or whatever, in their new plane? I would think from a marketing standpoint, you wouldn't want to have it be negatively compared to the same plane in gas form. Maybe they will be able to say it has slightly lower cruise speed, but it also is significantly more fuel efficient?? Jet A seems to cost the same as 100LL, so no benefit there. But if they could be run on something comparible to car diesel, then I think that would also be a great benefit ($2.80 versus $5.00/gallon).

Mike S · #5 10-26-2007, 03:32 PM

Quote:

Originally Posted by AndyRV7

Any opinion why Cessna would not put a larger displacement, or whatever, in their new plane? I would think from a marketing standpoint, you wouldn't want to have it be negatively compared to the same plane in gas form.

I suspect it was a lack of a certified engine availability.

frankh · #6 10-26-2007, 04:41 PM

At least i don't think so because the stuff gels up at low temperature. you can get additives but I don't know how effective an additive is down to say 10F.

Thats why the diesels will use JetA as that freezes at minus 60C I think.

Frank

airguy · #7 10-26-2007, 08:29 PM

More like -10C and -40C, for diesel and Jet A respectively, before additives - IIRC.

Dave_Boxall · #8 10-27-2007, 03:26 AM

The Theilert diesels (used in the Cessna) are certified for auto diesel and Jet-A1 or any mixture of the 2. There is a temperature limitation for any mix containing >10% diesel because of the gelling issue.

Generally anything that will run on Jet-A1 will be fien on road diesel (gelling aside), but the reverse is not true as Jet-A1 has lower lubricity so may increasing wear in the injector pump if it designed to be lubricated by the fuel.

Dave

SvingenB · #9 10-27-2007, 04:04 AM

Diesels run just fine here in -35C or colder in the winter. Paraffin oil is mixed into the fuel according to the season. Diesels runs just fine on 100 % paraffin oil as well (basically jet A). Some put a small dash (a few dl) of synthetic two stroke oil in the tank every now and then to lubricate the pump.

AndyRV7 · #10 10-27-2007, 05:28 AM

This has been educational. At least I understand what everyone is talking about now!

It seems like the only issue with the 100LL is that it is a GA fuel and that means it is not utilized in large enough quantities for someone to want to ake it. Interestingly enough, if it was used in larger quantities, I'm sure the lead issue would have been the next hurdle to have to be dealt with. I guess with such a relatively small community, we are flying under the radar, so to speak.

Thanks for all the answers.