To Treat or Not to Treat

Transcription

1 To Treat or Not to Treat Should I use diesel fuel additive or not? This is a question asked by many diesel owners, but one that for others, is a no-brainer. The problem is that, those who are absolutely sure what the right answer is, often have completely opposite answers. How can this be? Who can be trusted? Well, in the following I seek to shed some light on the issue in order for diesel owners to be able to make informed decisions. The first time I ever thought to use a diesel fuel additive was back in the 90 s when my Volkswagen dealer recommended it for my 95 Golf GL. They claimed it prevented wax formation in the fuel system. Believing them to be the experts, I complied. Well, for a little while. It generally seemed like an unnecessary expense which other diesel owners were not incurring; so eventually I quit, and I never seemed to incur any problems thereafter. I racked-up over 400,000 kilometers on that car before she lost a battle with a utility pole. After that I bought a used 1987 Mercedes 300D that I drove for some time, and then I got away from diesels for a few years. Eventually, the price of gas climbed, and the large gas-guzzlers I was driving started to wear on my patience and my pocket book, so I began to look at diesels again. Having 5 kids, it wasn t an option to buy a little Prius or anything like that, so I searched for 7-passenger diesels. To my surprise, there really weren t a lot of options in Canada or the US. It seemed the consumer market was decidedly anti-diesel. Meanwhile, Europe was

2 saturated with diesels. Ultimately, I settled in on a Mercedes R320 CDI because it met all my criteria: 7-passenger, all-wheel drive, and very fuel efficient. By this time however, during my research, I found that consumers were having a very different experience with diesels. Where in the past, it seemed like they just ran maintenance-free forever, now they were plagued by maintenance and mechanical failure issues. So much so, that many were trading their diesels in for gassers instead. In addition to this, in advertising and on forums, the discussion of diesel fuel additives had emerged and become very prominent. The problem I found, when I investigated this a little further, is that I couldn t seem to find a straight answer anywhere. In fact, to this day, if you skim the message boards and marketing you will still likely be just as confused as when you started. So, what changed in that period? A conventional diesel injection system consisting of a mechanical injection pump and simple injectors. Well, in 1999, the first common rail diesels came into the market, and by 2005, had become the fuel system of choice for most manufacturers. Common rail direct injection offered improved fuel economy and better performance, but this was at the expense of complexity. Instead of a mechanical injection pump that had fixed timing to the engine RPM, now a common fuel rail was pressurized to 20,000psi or more, and a computercontrolled unit injector (usually a piezoelectric injector) could inject at different timing and in multiple injections in a single stroke. All very cool. We are now seeing this technology becoming ubiquitous in tractors as well. The next thing that also happened in this period is new diesel emissions regulations. To clamp down on oxides of nitrogen, which are responsible for ground level ozone, was saw diesel engines fitted with EGR (exhaust gas recirculation), DPFs (diesel particulate filters), and DEF (diesel exhaust fluid). The principle behind these were; that the combustion of diesel fuel under normal conditions produced these oxides of nitrogen, but if we could lower the combustion temperature, these would be significantly reduced or eliminated. This was achieved by circulating some of the exhaust gas back into the intake (EGR). This unfortunately, had a nasty side-effect; soot. So, the solution to that was a filter (DPF) to remove those A common rail direct injection system uses a high-pressure pump to pressurize the fuel rail. Th e p iezoelectric injectors receive signals from th e control u nit th at cau ses th em to actuate and perform the fuel injection.

3 particles from the exhaust. Unfortunately, this also had a negative consequence; the filters would eventually get plugged and require regeneration, which was achieved by spraying raw fuel in the exhaust and burning off the particulate at high temperatures. This was obviously also an emissions issue. Then finally came along the diesel exhaust catalyst (DEF), where we could inject a urea-based solution into the exhaust and scavenge those nasty pollutants, and reduce the amount of EGR and regeneration cycles. Problem solved! Unfortunately, though, all this emissions equipment takes a toll on the diesel engine, primarily in the form of reduced power, efficiency, and oil contamination. And finally, there was another major change in this period. Ultra Low Sulphur Diesel (ULSD). Sulphur, being another pollutant, that needed to be removed and subsequently resulted in the advent of cleaner fuels. But, like we have seen already in other technologies, this came with a trade-off. The properties of sulphur provided a lubricating factor to the fuel. This was especially important in older diesels, because as my grandfather who was a diesel mechanic for over 40 years always told me, the diesel fuel is the only things that lubricates the injection pump. Now, a lot has changed since he retired about 30 years ago, including more precisely built diesels and more advanced lubrication systems, but one thing remains, there is still metal on metal inside that injection pump where no engine oil comes in contact. At any rate, oil companies and regulators were aware of this, and so additives were formulated to correct for this and the other altered properties. But getting to the point here, if any one of these 3 things had occurred on its own, and subsequently resulted in widespread issues, we would know exactly where to point the finger. But unfortunately, it didn t happen that way, which makes it difficult to ascertain the cause. Who in their right mind would ever change so many variables at once? [This is where the conspiracy theorists start chiming in.] But in reality, there was quite an abundance of research performed on this, but it never made it to the consumer level, much like the research on saturated fat and transfat. It gave way to marketing, and market pressure limitations, and ultimately, everyone was able to point the finger at someone else. At any rate, the issues seem to be more prominent in North America than in Europe. So, what s the difference? Are Europeans better at making diesels than North Americans? No, because the European made diesels that come over here suffer the same fate, and sometimes even more so. The real problem is, evidently, the quality of the diesel fuel. As I mentioned above, ULSD fuel had been ushered in during this period, and this was done on both sides of the pond. So how could this possibly be the problem? Well, in simple terms... the additives. Additive packs are formulated to improve lubricity, cetane number, water dispersion, carbon deposits, cold flow properties, and to control fungal growth. But they cost money. They add an incremental cost on each litre (or gallon for ya ll South of the border) of fuel. The properties these additives impart on the fuel can be scientifically measured and adjusted, and have been well characterized. As well, there is little to no, proprietary secrets regarding this, it s all in the

4 public domain. So, the final determination of how much additive goes into your fuel is the result of government regulation and cost. And as we know in North America, people are very sensitive to the cost per litre (or gallon) of fuel, so it s not just a matter of adding more and charging more. The two key aspects I want to focus on are lubricity and cetane number. Lubricity Lubricity can be measured in a test called the High Frequency Reciprocating Rig (HFRR). This method is the industry standard and tests the physical properties of a lubricate to resist wear by applying pressure and friction against two metal surfaces in the presence of the lubricant and then measuring the resulting wear scar. Few regions in North America have a minimum lubricity requirement, and California is one of those regions, requiring a maximum 520 micron scar based on the ASTM D6079 method. Back in 2007 an independent blind study of various brands of consumer additives was conducted by Dieselplace.com. You can visit it by copying this link into your browser: maintenance-fluids/ lubricity-additive-studyresults.html In this diagram can be observed the complexity of a simple diesel injector. Metal components are machined to extremely tight tolerances and are in direct contact with each other while actuating. Inside the injector, the only lu bricant is th e fuel itself. At 2,500rpm a conventional diesel injector will actuate 20 times p er second; a p iezoelectric injector may actuate up to 80 times per sec. According to this study, the baseline pump fuel they tested produced a 636 micron scar. They claim that engine manufacturers want to see a maximum 460 micron scar, which is confirmed in the document Diesel Fuel Injection Equipment Manufacturers Common Position Statement issued June 2004 jointly by Delphi, Bosch, Siemens, Denso, and Stanadyne. This coincides with the European EN 590 standard of 460 microns. The manufacturers states that unless a minimum quality of lubricity can be maintained, they cannot predict or achieve modern fuel system reliability. California s 520 micron scar requirement is the best in the US however it still falls short of the EU standard and the manufacturers desired standard. In Canada, the situation is worse, because there is no enforcement, and compliance is voluntary. The Dieselplace.com study showed that a 2% blend of biodiesel exceeded the lubricity properties of all other consumer products and achieved a wear scar of 221. Coming in second in their test was Opti-lube XPD with 317. FPPF and Opti-lube Summer blend, were the only other two that achieved the 460 or better wear scar based on the recommended treatment rates. And in fact, there were several that worsened the lubricity properties of the base fuel. Based on this, it is clear that not all additives are created equal. Further to this, oil companies are quite silent on the lubricity properties of their fuels.

5 What is the takeaway so far? Fuel lubricity is a real issue, such that some jurisdictions are regulating it. Manufacturers say it s an issue, and realworld experiences suggest it s an issue. If you are in a region that does not regulate fuel lubricity, and you know that your fuel has no biodiesel blended in, then you cannot be sure that the diesel s lubricity properties are sufficient to protect your fuel system. You should probably treat it with an additive. Wear that affects performance and fu nctionality may not be discernable to th e naked or u ntrained eye. Now, there is no need to panic. This does not mean that if you miss a tank here and there, or if you don t treat at all, that your engine will suddenly explode. You will likely incur higher repair costs during the course of ownership. Only in rare cases do people experience catastrophic fuel system failure. Cetane? What is this stuff? Actually, it s not stuff as all, it s a numerical value assigned to the ignition quality (or ignition delay) of diesel fuel. It s basically the inverse of octane, where a high cetane number indicates more rapid ignition and octane is retarded ignition. Again, there is a method to test this, which uses an actual test engine to measure the real-world values. There is also ongoing research to develop a quick chemical analysis method, but I don t think they re quite there yet. Of an additional note, some use the term cetane synonymously with Hexadecane, but this is not universal, and may be misleading in a conversion about cetane number. Engine sludge is visible on these valves. Sludge can deposit throughout the engine and can block the flow of oil. This can result in the engine being starved of oil, and consequently cause the engine to seize. A low cetane number (CN) is not directly harmful to your engine, but rather, it is the secondary effects that one needs to be concerned about. A low CN will result in not all the fuel being burned, which in turn produces soot. For all diesel engines, some of this soot ends up in the engine oil because the high compression of the diesel engine forces some of the gasses past the rings. This is why diesel engine oil is always so black. The problem with this is that it collects in the oil, causes and accelerates oxidation, causes oil thickening, and if it reaches a tipping point, causes rapid sludging. In oxidation, the lubricating properties of the engine oil are reduced. This is clearly bad parts wear faster and require replacement sooner. Sludge is a nightmare and can in extreme cases result in rapid and catastrophic engine failure. In fact, you can go on some Mercedes forums and read all about the personal experiences. As a result, if

6 your fuel has a low CN, you will require more frequent oil changes to preserve your engine s performance and longevity. If you have a newer diesel engine that has the above-mentioned emissions equipment, the extra soot production will plug your DPF sooner, requiring more frequent regeneration cycles, and ultimately shortening the overall life of the DPF. DPFs are not cheap. Many people report complete failure within the federally mandated emissions equipment warranty period, only to find out, that this legislation doesn t specifically include the DPF. They then find themselves at the mercy of manufacturer to voluntarily replace the failed DPF. It is reasonable to expect between $1,500 and $4,000 for a DPF replacement. There are also specialty cleaning services for DPFs, but these require removal, and as a result, are typically only used for large commercial vehicles such as semi-trucks (aka big-rigs, tractor-trailers, etc). Coking of an EGR valve. A very common failure in diesel engines. As a final note on the consequences of low CN, it also results in a higher incidence of coking in the cylinder and on the injector. So, in general, it is better to have a higher CN than a lower one. Higher CNs improve fuel economy, responsiveness, and reduce production of soot and oxides of nitrogen. The research of these benefits can be viewed in a number of studies performed by Sandia National Laboratory in the US and Pembina Institute in Canada; not to mention numerous others around the world. This is so widely accepted that I m going to state it as a given, and move on. CNs vary greatly in North America by region and retailer, but are not typically published. This is because, while some additive is added in at the bulk filling depots, some is also added at the retail pump stations. The US requires a minimum of CN 40 and this is regulated and enforced. In Canada there is a national voluntary standard of 40 that is not enforced. The European EN 590 standard is 51, and is strictly enforced. According to Sandia Nation laboratory report Effects of 2-Ethylhexyl Nitrate on Diesel-Spray Processes, typical US CNs are between 42 and 50. Anecdotal reports from consumers who have done their own information requests from fuel suppliers, have confirmed this to the present day. Without getting into it much further, the study continues to describe the process by which 2- EHN (2-Ethylhexyl Nitrate) improves the ignition process but does not actually increase the amount of available energy, this has its most prominent impact during start-up. This study as

7 well as other studies done by Sandia, indicate that in order to achieve a 10-point rise in CN it was necessary to use 4,000ppm of 2-EHN. The International Journal of Modern Engineering Research s study Effect of CETANE Improver Additives on Emissions, states that after CN 55 there is no further improvement in performance or emissions. There is no known detriment to higher CNs. Based on typical industry CN across Canada and the US, we can expect that a 10-point rise in CN will get us to at least the European standard. With 2-EHN, being the most prevalent cetane improver, what does that mean in actual dose volumes? Well, that means 40mL per 10L of diesel fuel, that s about 1/2 oz per gallon. In other words, 320mL per 80L, and 10.24oz for 20 gallons. But that doesn t mean that we can go to our local auto supply and pick up a bottle of something and put 320mL in and expect to achieve that much CN improvement. Why? Because these off-the-shelf products are not pure cetane improver. In fact, it is rare to find one that is more than 50% 2-EHN by volume, and most fall in the range of 10 15%. So, what does that do to dose rates. Well, if you have a product that is 15% 2-EHN, then you would need to add 2.13L of additive to get the 10-point rise in 80L of fuel. For 20 gallons of fuel you would need over half a gallon of additive. In my personal search for cetane improvers, which included contacting the suppliers myself, I have not encountered a single brand whose recommended dose would achieve a 10-point rise. Unfortunately, when soliciting advice for cetane improvers you will get all sorts of different responses, and in the end you will probably be as unsure as when you started. I personally have been dosing my fuel to achieve the 10-point raise for three years now. In addition to this, I conducted a trial with a truck driver at that same high dose rate. Basically, you may or may not notice a different feel to your vehicle you are more likely to notice a difference, if after dosing for a while, you forget one tank. In this case your vehicle typically feels marginally more sluggish - some people may not notice. You also may not be able to notice a fuel economy improvement because there are just too many variables. You would have to track your mileage over a long period of time and analyze a sizeable number of data points; but in reality, it will save you between 5% and 10% in fuel. For comparison purposes, a moderate headwind on the highway will easily cause you to consume an extra 20% fuel. One thing that is significant however, is soot production. For emissions systems with a A cut-away of a p lugged DPF. A common meth od of regeneration is by performing an additional fuel injection during the exhaust stroke to deliver fuel to th e DPF and allowing it to burn off the soot. differential pressure sensor (DPS) that initiates a regeneration cycle based on how plugged the DPF is, you may experience a 66% reduction in the frequency of regeneration cycles this is based on my real-world trial.

8 If you miss a treatment of 2-EHN, or don t treat enough, or don t treat at all, will your engine explode? Not likely. If you don t treat, and you cannot confirm the CN of the fuel you use, you will likely incur higher repair and maintenance costs. On an older diesel with no emissions equipment, you won t likely notice anything, except more difficult cold starts without treatment. In any diesel, when consistently using low CN fuel, you should change your oil more frequently to prevent sludge, which can seriously harm your engine. So, what is the final take away from all this? There is merit in both lubricity additive and cetane improver additive Not all additives are created equal Proper additives will benefit any engine where the fuel quality is insufficient to provide protection for wear, emissions components, and sludge. You are likely to incur higher repair and maintenance costs with untreated or poorly treated fuel