A few days ago I've noticed that my diesel car started to produce some strange rumbling/ rattling vibrations at the low revs. It manifested in a similar way as you would experience the fault ignition cable or a fault spark-plug on a car with a petrol engine.
The fumes from the exhaust were unusually hot and the most logical explanation was simple: some of the diesel went to the exhaust without being burnt.
The solution is to use some steemcleaners, I mean injection cleaners.
There is no need to call steemcleaners, this post will be "clean"
For the last two years, I was conducting the research for petrochemical industry and I'll devote 2-3 posts to this part of my life. CV is a simply obsolete way of communication.
(*yes, I know, my career is like a rollercoaster: molecular biology --> spectroscopy --> math --> asphalt but unlike the rollercoaster, it also included some branching as well).
Types of deposits and the problems related to deposits
There are 3 significant regions in the cylinder chamber that are exposed to slightly different conditions (different temperature is the main factor) and consequently forming 3 types of deposits that could be classified according to porosity. Numerous studies have been done that included AFM, FTIR, Raman, NMR and I played a little bit with EPR, because the deposits are forming stable organic radicals.
- deposits on the intake valve (the one that made my engine running badly)
- deposits on the cylinder head (check the diagram)
- and the deposits accumulated on the top of the piston
This various porosity will affect chemical properties of the material and produce contradictory effects once we discuss the cleaning methods.
Deposits themselves can negatively affect the performances of the engine by simply blocking the valves to move freely. Some "hot spots" could be formed and create the unwanted ignition (this could be prevented by using the fuel with the higher octane number). And of course, the deposits could form the insulation layer. Keep in mind that bad ignition = more pollution and less power...
What is the composition of injector cleaners?
This is not a sponsored post, thus I have no intentions to advertise any of those products.
Generally speaking, all products of this class have a very similar composition, thus buy the one with the nicest name and with the reasonable price.
PEA (polyether amine) and PBA (polybutene amine)
Those are the main ingredients in all injection cleaners because those are well-known industrial detergents.
There are not too many substances that could be dissolved in fuel, ignited and yet retain the main pourpose.
Isopropyl alcohol (IPA)
As a biologist, many times I experienced the problem how to dissolve some substance in water that is (almost)not soluble. The solution is very simple: dissolve the substance in a small quantity of a suitable solvent (like DMSO) and then put that mixture into the water - it will work.
The most common impurity in fuel is - water. Water can make all sorts of problems. It could freeze in lines during the winter, it will destroy the surfactant layer it will make several problems if it's ignited in the cylinder *(unless we are talking about very strange BMW M4 CS).
So the idea is to keep the water in some small droplets and to mix it with the fuel as best as possible.
Isopropanol, IPA, is perfect for this purpose for several reasons:
- it doesn't evaporate easily
- it mixes with water, ethanol, ether, and chloroform while dissolving fats, oils and resins
- it lowers the freezing point of the fuel
Conclusions from the studies:
As you can see, fuel manufacturers have to make compromises. They need to add additives, including the detergents and IPA.
But... If there are way too many detergents, those will ruin the engine oil. Both the detergents and IPA will cause the formation of deposits on the top of the pistons. If they remove all the detergents there will be the deposits on the intake valves. And if there is no IPA, water will ruin, well, everything.
Let's see what was published in one of only a handful of studies (for petrol engine!, but it's similar)
We observed that for the PEA additives the average reduction of the mass of the intake valve deposits was 73% with respect to the base fuel deposits. This reduction was accompanied by 21% increase of the mass deposited on the cylinder heads and piston tops. 
So, what should we do in practice?
First of all, check which brand of fuel is good for your car. My Alfa prefers Shell, Shell for her is like the chocolate for me. And the Total fuel is considered to be the broccoli for her. It doesn't mean that some brand is "bad", it means that it's not optimal for your car.
There is no need for "Premium" fuel if your engine belongs to the older generation.
If your car is new there is no need to start with the additives from the Day 1 because your valves are clean (there is nothing to clean there). Using too many additives will make more deposits on your pistons.
Of course, use the cleaners regularly (in my case, 3-4 times per year). You will increase the power, increase your mpg (percent or two) and reduce the pollution.
- A Fuel Additive Concentrate for Removal of Injector Deposits in Light-Duty Diesels 841349, link
- A Survey of Gasoline Fuel Deposit Control Additives in the Retail Aftermarket: Performance Claims vs. Chemistry 982712, link
- Evaluation of the Effect of Fuel Composition and Gasoline Additives on Combustion Chamber Deposits 962012, link
- Zerda, T. W., Yuan, X., & Moore, S. M. (2001). Effects of fuel additives on the microstructure of combustion engine deposits. Carbon, 39(10), 1589-1597. link
- Website about the industrial application of isopropanol, link
*Keep in mind that the vast majority of industrial research is kept confidential and never published in scientific journals, even at the level of general concept thus it's very difficult to find the proper references. Most of the time, it's easier to do the experiment from the scratch.