Volvo Owners Club Forum - View Single Post - Engine: D5:

Jim314 · Jun 19th, 2010, 11:25

Here's the story as I understand it. I don't think biodiesel causes extra soot over petroleum diesel.

The claim by Volvo was that some diesel at the ordinary pump contains 5 - 8 % biodiesel, but this seems unsupported by any evidence. I don't see any reason why oil companies would add any biodiesel to their fuel. Biodiesel costs more than petroleum diesel and is not a product of the oil companies. And if the retail sellers of fuel would add biodiesel, wouldn't they have to report this to regulatory authorities and to the consumer? In the US petrol pumps for motor cars state that the fuel may contain up to 10 % ethanol. By contrast diesel pumps do not state anything about the possible presence of biodiesel.

In the US one has to go to identified purveyors of biodiesel to get either pure biodiesel or biodiesel mixed with petroleum diesel. Some people add biodiesel to their fuel tank themselves in the belief it would be a benefit to the environment. And biodiesel mixes up to 10 % or so are apparently fine in any modern diesel unless the fuel system uses an extra delivery of fuel into the cylinders to raise exhaust temperatures to regenerate a DPF.

Here is the problem as I understand it. There are two ways to introduce extra fuel into the exhaust stream to raise the exhaust temperature:

(1) Use a separate injector located in the exhaust manifold (or pipe?) to introduce extra fuel into the exhaust stream. This system is used on certain large diesel commercial engines and allows the use of biodiesel mixes even with a DPF.

(2) Program the fuel system to use the regular injectors to give an extra squirt of fuel into the cylinders during the exhaust stroke (during the DPF regeneration cycle only). This mixes with the exhaust gasses and is pushed out by the piston as it expells the exhaust gasses. But after the power stroke the insides of the cylinders are relatively cool and if fuel containing biodiesel is sprayed into the cylinder, the biodiesel (which is less volatile than petroleum diesel) condenses to or remains a liquid on the cylinder walls. The petroleum diesel is volatile enough to be gasified and get swept out the exhaust valves.

But as the piston advances the liquid film of biodiesel on the cylinder wall is forced past the compression and oil rings and gets into the sump. I don't have it straight whether this is thought to occur on the exhaust stroke or on the subsequent compression stroke.

So over time the oil in the sump gets contaminated with fuel and the oil level in the sump rises to a level significantly above the max. It can supposedly rise so high that the sump oil begins to squeeze by the rings and thereby give rise to a runaway diesel where the engine is fueled through the sump, speeds uncontrolled to high power output and self destruction.

Jun 19th, 2010, 11:25	#29
Jim314 Premier Member Last Online: Nov 20th, 2018 01:45 Join Date: Feb 2009 Location: Dallas, Texas	Here's the story as I understand it. I don't think biodiesel causes extra soot over petroleum diesel. The claim by Volvo was that some diesel at the ordinary pump contains 5 - 8 % biodiesel, but this seems unsupported by any evidence. I don't see any reason why oil companies would add any biodiesel to their fuel. Biodiesel costs more than petroleum diesel and is not a product of the oil companies. And if the retail sellers of fuel would add biodiesel, wouldn't they have to report this to regulatory authorities and to the consumer? In the US petrol pumps for motor cars state that the fuel may contain up to 10 % ethanol. By contrast diesel pumps do not state anything about the possible presence of biodiesel. In the US one has to go to identified purveyors of biodiesel to get either pure biodiesel or biodiesel mixed with petroleum diesel. Some people add biodiesel to their fuel tank themselves in the belief it would be a benefit to the environment. And biodiesel mixes up to 10 % or so are apparently fine in any modern diesel unless the fuel system uses an extra delivery of fuel into the cylinders to raise exhaust temperatures to regenerate a DPF. Here is the problem as I understand it. There are two ways to introduce extra fuel into the exhaust stream to raise the exhaust temperature: (1) Use a separate injector located in the exhaust manifold (or pipe?) to introduce extra fuel into the exhaust stream. This system is used on certain large diesel commercial engines and allows the use of biodiesel mixes even with a DPF. (2) Program the fuel system to use the regular injectors to give an extra squirt of fuel into the cylinders during the exhaust stroke (during the DPF regeneration cycle only). This mixes with the exhaust gasses and is pushed out by the piston as it expells the exhaust gasses. But after the power stroke the insides of the cylinders are relatively cool and if fuel containing biodiesel is sprayed into the cylinder, the biodiesel (which is less volatile than petroleum diesel) condenses to or remains a liquid on the cylinder walls. The petroleum diesel is volatile enough to be gasified and get swept out the exhaust valves. But as the piston advances the liquid film of biodiesel on the cylinder wall is forced past the compression and oil rings and gets into the sump. I don't have it straight whether this is thought to occur on the exhaust stroke or on the subsequent compression stroke. So over time the oil in the sump gets contaminated with fuel and the oil level in the sump rises to a level significantly above the max. It can supposedly rise so high that the sump oil begins to squeeze by the rings and thereby give rise to a runaway diesel where the engine is fueled through the sump, speeds uncontrolled to high power output and self destruction.