Noisy combustion (popping, cackle) during warm-up

[philip]

in a cold combustion chamber is that a large amount of fuel vaporizes and mixes with air before ignition takes place. When ignition begins, the vaporized fuel and air mixture burns rapidly, producing a large pressure rise, a high peak pressure

It's curious why you started getting poppings and knocking after installing rebuilt injectors.

First, notice the NAPA fuel treatment label says the product contains primarily KEROSENE which is a common cetane improver and gel point lowering agent.

Next, I notice the cold engine cackle / popping behavior with winterized diesel fuel use. Same thing the previous winter. And when I recently mentioned it to the previous owner / original buyer, he said the truck had this behavior from new.

One obvious assumption would be that the new injectors deliver more fuel, or atomize fuel MUCH BETTER than the factory one? Wouldn't a more perfect vaporized fuel and air mix ignite a little bit earlier than not so well vaporized? I am just thinking deductively here.

The reason for the cold cackle/popping is two part. One: using fuel that ignites more easily, Two: the cold combustion chamber surfaces moves the point of igition closer to TDC which means the combustion chamber pressure is higher and more fuel has been injected by the time ignition does occur ... resulting in a more sudden and violent combustion. Temperature does not affect injection timing but ... temperature does affect ignition timing after injection begins. Refer back to the red print in the first post in this thread.

IMO, I'd rather have a little bit of smoke coming from the tail pipe than knocking at lower temperature and I'd look for used injectors after you exhausted all other possibilites and still having this problem.

You still do not understand the phenomenon. Providing a richer mixture when cold AGGRAVATES the phenomenon.

Used injectors solves nothing. Remember, injector pop-off pressure affects actual injection timing. Higher pop-offpressure = later injection.

Let me describe what's going on differently. Let's say the engine is at normal operating temperature, that fuel injection starts at 20 degrees BTDC, and that air compressed by the piston is hot enough to ignite the first bit of fuel injected at 15 degrees BTDC.

Now, lets take a stone cold engine. Obviously all the cold combustion chamber surfaces absorb quite a bit of heat from the air being compressed by the piston. So now ... the compressed air does not attain sufficient heat to ignite diesel fuel until 5 degrees BTDC. The differences are: instead of only 5 degrees worth of fuel being present before ignition begins, now 15 degrees worth of fuel is present. PLUS, with the piston being closer to TDC, the pressure is higher than it would be otherwise. The larger amount of fuel under higher pressures explodes ... instead of burns. There's your cold combustion knock, which can easily be aggravated by cetane "improvers" which make the fuel more combustable. This phenomenon can poke holes in pistons.

Again, refer back to the first post in this thread.

[Zoltan]

Thanks for making this more understandable. I did suspect that some of the stuff in the treatment increases cetane number, although this wasn't stated on the bottle specifically. Can you find "unwinterized" diesel in your area?

The fuel pump decal in our area states the sulfur ppm value, therefore adding the fuel additive is not always necessary. Most of the pumps here still sell the 500 ppm sulfur diesels. I add the treatment to every 2nd tank to keep the injectors clean.

[philip]

Thanks for making this more understandable. I did suspect that some of the stuff in the treatment increases cetane number, although this wasn't stated on the bottle specifically. Can you find "unwinterized" diesel in your area?

California is a peculiar place. The State Air Quality agencies care only that your driving does not pollute any more than their ever tightening standards. So ... winterized and boutique formulation motor fuels are found in higher altitudes and metropolitan areas respectively nearly year round. And with the new Ultra Low Sulphur Diesel fuel just beginning to show up at the pumps (15ppm), there is plenty of concern from fleet managers just how well older equipment will tolerate the reduced lubricity without owners contributing lubricity additives. (See "Ultra Low Sulphur Diesel Article I and II).

With the new injectors I installed in my truck, I've been using a lubricity improver. (See: Ultra Low Sulphur Diesel Article I). Since the STP product is rare if not discontinued, I switched to the Stanadyne approved product.

The fuel pump decal in our area states the sulfur ppm value, therefore adding the fuel additive is not always necessary. Most of the pumps here still sell the 500 ppm sulfur diesels.

With 500 ppm sulphur content, you need NO lubricity additive and by a WIDE margin. That much sulphur does contribute to visible exhaust soot.

I add the treatment to every 2nd tank to keep the injectors clean.

Injector cleaner is a feel-good thing to lighten your wallet. Actually cleaning your injectors is a process requiring dental tools and equally skillful scraping and picking.

Refer to thread: SD22 Injector Experience

[asavage]

With 500 ppm sulphur content, you need NO lubricity additive and by a WIDE margin. That much sulphur does contribute to visible exhaust soot.

Low Sulfur Diesel (ie 500 PPM max) was introduced in the US in about '91, and there was hue & cry about it. I recall a couple of articles I read which stated that injection system failure (accelerated wear) would be common when LSD was introduced. Anecdotally, there seems to have been some IP problems for a couple of brands. The process to reduce sulfur content in common use by refiners at the time reduced the lubricity of the fuel.

Sulfur is a factor in PM? First I've heard. Any chance you've got a reference for that?

[philip]

Low Sulfur Diesel (ie 500 PPM max) was introduced in the US in about '91, and there was hue & cry about it. I recall a couple of articles I read which stated that injection system failure (accelerated wear) would be common when LSD was introduced. Anecdotally, there seems to have been some IP problems for a couple of brands. The process to reduce sulfur content in common use by refiners at the time reduced the lubricity of the fuel.

Sulfur is a factor in PM? First I've heard. Any chance you've got a reference for that?

I recall that milestone. The company I was driving for at that time experienced no fuel system failures that I ever heard about. But then again, all our equipment was turned back in every three years or 500k miles. We had no dated equipment.

Soot and Sulphur. I must own some lazy thinking here. I associate fuel sulphur compound (SOF) reductions and concurrent fuel system improvements to tolerate less lubricity and produce lower emissions as a net reduction in sulphur laden exhaust soot. Academically, there is a more specific correlation between fuel sulphur compounds and exhaust sulphur emissions than there is between fuel sulphur compounds and exhaust soot in general.


http://www.scienceinafrica.co.za/2002/march/turbo.htm

"Sulphur in diesel contributes towards the formation of the acid rain causing and lung-damaging pollutant, sulphur dioxide. It is also directly related to the amount of soot formation in a diesel engine and hence also the amount of particulates introduced into the atmosphere. In addition to polluting the atmosphere, these chemicals pollute the vehicle's engine itself: causing changes in the lubricating oil composition as well as the poisoning of the exhaust treatment catalysts, degrading their performance. In the long term, these chemical changes reduce the efficiency of the oil, meaning a need for frequent oil changes. Low sulphur fuels, such as Sasol TurboDiesel™ extend the life-span of the oil as it is not degraded as quickly. Longer oil-change intervals translate to direct savings of time and resources."

[philip]

I have found two "cetane improver" formulations to exacerbate ignition lag knock when mixed "lean". But when mixed "rich" the cold combustion knock decreases. When I say "rich" I mean 1oz per 2 gallons D2 (the ultra low sulfur stuff we now have).

Hmmm