Toyota made ceramic pre-cups - 2L-THE (1 Viewer)

[GTSSportCoupe]

I always thought ceramic pre-cups would have many advantages for the IDI turbo diesel engine. Browsing some SAE papers this morning, I discovered that Toyota did include them in at least one engine. I've attached the paper if anyone is interested. The material is Silicon Nitride. I believe this material is also used in Toyota's ceramic turbo-chargers.

Turns out the engine Toyota used the ceramic pre-cups in is the 2L-THE, which is a more advanced version of the 2L-TE. From the little information I can find on people who have owned a 2L-THE, the new head with ceramic pre-cups is a big improvement in terms of power and lower coolant and EGT temps (over the basic 2L-TE head).

Makes me wonder why 2L-TE owners don't upgrade to the 2L-THE head instead of the 3L head? If the head ever goes in my LJ78, I may try to track down one of these heads with the ceramic pre-cups...

Also makes me wonder why Toyota didn't put ceramic pre-cups in all the 2L-TE powered vehicles, or for that matter, into other engines like the 1HZ.

 

[DanS HJ-45]

Fascinating.

I'm thinking exactly the same. If my head ever cracks, I'd love to track one down.

Dan

 

[gerg]

I find this interesting as when I was talking with Dave, owner of passenger performance who does high output vw diesels, he said that he had multiple back to back Dino's showing a significant loss of power and higher egts when pre cups were ceramic coated. His thought was that the ceramic coating interfered with heat transfer to the new air fuel mix in the swirl chamber thus delaying ignition as well as slowing the flame front propagation. I can see insulating the cup from the head itself, but the cup needs to absorb a lot of heat and readily transfer it to the air fuel mix. Developing barriers between the cup and the head as well as insulating the upper chamber is a win win.

 

[GTSSportCoupe]

Fascinating.

I'm thinking exactly the same. If my head ever cracks, I'd love to track one down.

Dan

The Toyota part # from ToyoDIY is 11101-54140. You can look up 1991 LS131 Crown with 2LTHE for more info on ToyoDIY. Without seeing the head, there is no way to confirm if it is actually interchangeable with the 2LTE version, but it sure would be neat to know. There is a fellow on the Toyota Diesel forum who installed one of these engines into a pickup and was very happy with it: http://toyotadiesel.com/forums/showthread.php?3844-2L-THE-on-the-road&highlight=ceramic First post is a promising read.

In my searching I discovered the Russians seem to import Crown's with these engines. Using a website translator I learned that the 2L-THE does not have the head crack problem of the 2L-TE (from what they are saying anyhow). There may have been other factors redesigned in the head (along with allowing the ceramic pre-cups) that improved it's resistance to cracking.

I've also learned this 2L-THE engine had a ceramic turbo (for quicker spooling), a higher volume and pressure injection pump, and different injectors. The ECU would also have been tuned to make the best of all these features.

I find this interesting as when I was talking with Dave, owner of passenger performance who does high output vw diesels, he said that he had multiple back to back Dino's showing a significant loss of power and higher egts when pre cups were ceramic coated. His thought was that the ceramic coating interfered with heat transfer to the new air fuel mix in the swirl chamber thus delaying ignition as well as slowing the flame front propagation. I can see insulating the cup from the head itself, but the cup needs to absorb a lot of heat and readily transfer it to the air fuel mix. Developing barriers between the cup and the head as well as insulating the upper chamber is a win win.

It may have to do with the type of ceramic used. The interwebs say Silicon Nitride has a thermal conductivity of up to 43 W/m.K. Nickel is 90.9 and Iron 80. So they are in the same order of magnitude. The modern after market ceramic coatings are far more resistant to heat transfer from what I can tell. Also, only the lower part of the 'swirl chamber' is ceramic in the Toyota application; not sure how this would play into it.

Looking through the article again, I think what Toyota was getting at with this innovation was not so much an insulating factor, but more the resistance to higher cylinder temperatures. So this basically allowed them to run more boost/fuel etc., making more power without cracking pre-cups.

On an aside, one thing I've always found interesting about the 2LTE, is the pre-cups almost never crack, where in a 3B, it is far more common. I attribute this to the 2LTE loosing a lot more heat from the pre-cups into the head, and thus causing the other temperature related issues such as localized boiling and hot spots (resulting in cracking). Better to crack a pre-cup than a head...

 

[gerg]

Ahh so it's conductivity is actually really good. Much better than inconel or stainless.

 

[keving]

What is the metallurgical composition of regular pre-cups? Say on a Regular L or B series diesel

 

[GTSSportCoupe]

For those with a technical interest in diesel technology, I found another article (attached) on the ceramic pre-cup technology. This article discusses the performance of the ceramic pre-cup vs steel pre-cup. Some VERY cool info. If not for the cost, I think ceramic IDI technology would compete with DI technology.

I quote:
"
The experiments were carried out using two types of divided chambers, that is, the swirl chamber made of ceramics and that made of steel, to examine the the effects mentioned above. In case of ceramics swirl chamber, the vaporization of fuel oil is promoted more, the vaporized fuel oil spreads more, the ignition delay is shorter, the maximum cylinder pressure, the initial rate of cylinder pressure rise, the initial heat release rate and the maximum heat release rate are higher, the duration of combustion is shorter, the flame spreads more, the region of high flame temperature is
1larger, the stabler combustion is maintained until the flame vanishes, and the soot is distributed in the wider zone than those in that of the steel swirl chamber.
"
and my favorite:
"
The phenomena in this chamber seemed to simulate those in the piston cavity of DI diesel engine.
"

I inquired with Rocky Mountain Imports to see if I could get the 2L-THE ceramic precup head ordered in. Answer, yes they can get it in. First price that came up was ~$2500, although he figured he could get it cheaper elsewhere with some hunting around. Hands down I'll be buying this head if mine cracks someday.