By Paul Dawson, BRP Australia Pty Ltd.

Transcription

1 By Paul Dawson, BRP Australia Pty Ltd. It seems we re always complaining about fuels. For as long as many of us can remember there's always some application that's not happy with current fuels. While today s fuels work great in most engines, they sometimes have problems in some applications, especially those applications that are not mainstream, like boating. And there s good reasons why it s difficult to make fuel suit everyone perfectly. Crude oil, or more correctly Petroleum, has very complicated chemistry that makes it near impossible to get an ideal mix, as the requirements change with the application, the season and even temperature. Up to 100,000 different chemical compounds are contained in petroleum, depending on where in the world it came from and what processes are used to refine it.

2 We create our fuels by distilling petroleum, that is heating it and allowing the different compounds to condense at different heights in the refinery tower. Of the 100,000 HC compounds, petrol is but a small fraction, just those molecules with between 5 and 12 carbon atoms, but even then there s about 500 chemical compounds to chose from. After simple refining (distillation) several other chemical processes are also used to convert more of the products into the most common fuels petrol and diesel. In the end nearly half of every barrel of crude goes into petrol type fuels. Petrol and diesel together make up nearly 75%. To understand why modern fuel can sometimes be a problem, let s look at history in recent decades and review the major changes, for outboards. In the 1970 s large outboards (those over 115HP) required 94 octane (RON) fuels, so the standard fuels of the day could not be used. All larger outboards used Super fuel. The first big change occurred in 1986, when all cars were required to be equipped with a catalytic converter, so Unleaded fuels needed to be easily available. The old Standard was replaced by ULP. Because ULP was to be the most commonly available and used fuel, all Evinrude and Johnson (and most other brands) modified their engines for reduced octane demand. All models since 1986 have been designed for ULP. In the mid 1990 s came RFG, (or ReForulated Gasoline). This was intended to add some oxygen to the fuel to aid combustion and make catalytic converters work well over a wider range of conditions. The extra oxygen was added firstly with MTBE, then when MTBE gained a bad reputation for tainting ground water, we switched to Ethanol. Both add oxygen to the fuel. But ethanol is really not a new idea.

3 In the 1930 s there were several concerted attempts to market Ethanol in fuels, usually to extend our oil reserves and help farmers. The idea of using Ethanol as a fuel goes back a long way. Even Henry Ford promoted it s use in the 1890 s as a clean and plentiful fuel. Closer to home E10 was used in QLD for almost 30 years primarily to help the local Sugar Cane industry. However, ethanol could not usually compete on price with mass produced oil, so until relatively recently when we decided to use it as a green fuel, it had almost disappeared in the market place. Now today Ethanol production is a large and rapidly growing industry all around the world. Many Governments are mandating it and the infrastructure to produce it rapidly increasing, so it looks like there ll be a lot of ethanol in our future. Brazil mandated Ethanol in all fuels beginning in the 1970 s and today they are leaders in its production and use. All vehicles in Brazil run on 24-26% ethanol fuels and some are capable of running well on 100%

4 An example from closer to home, NSW. The NSW State government requirement for Ethanol extended fuels is now legislated to be to a certain percentage of all fuel sold, beginning at 2% in 2007 and progressing to 6% in 2011 In 2012 all ULP is to be only E10. Governments are advising applications, but in very general terms. For petrol powered road and farm vehicles, and machinery, E10 is promoted. For aircraft it is NOT recommended because of the altitude and temperature changes that aircraft regularly experience. Plus, fuel used by aircraft is subject to greater distribution controls and must be kept separate from other fuels. For outboard boats it will be difficult to avoid Ethanol fuels. We regularly refuel our boats in the same place as we do our cars, plus all modern outboards are designed to run OK on E10. The main potential problems for marine use relates to storage. As they say There s no such things as a free lunch, there s plus s and minus s to the Ethanol argument, especially for the marine application. Plus - The ethanol reduces our reliance on imported crude oil, always a good thing. Ethanol fuels, with their oxygen content, assist combustion over a wide range of usage. Emission of HydroCarbons and Carbon Monoxide are reduced. (CO2 emissions are about the same as straight petrol). Ethanol is grown from renewable resources, so we can control our costs. Minus Ethanol has a lower energy content than petrol, so the fuel to air ratio (mix) must be altered for proper operation. Ethanol itself has a lower evaporation than petrol, but when mixed with petrol the combination actualy has more evaporation. Oil companies must make changes to petrol that will have Ethanol added to ensure we do not get vapour lock in summer or hard starting in winter. Ethanol is more corrosive than petrol because it holds more water content and is a better solvent, so it can shift dirt in the fuel system that petrol left alone. When the water content reaches a certain level, the ethanol (and the water) separates from the fuel. This is the most likely problem we will experience in marine applications. So let's look at these potential problems in more depth.

5 Ethanol has about 2/3 of the energy of petrol, so requires different fuel system calibration. The blue line on the chart shows the chemically correct fuel to air ratio required with different percentages of Ethanol. E10 is within the range most modern engines can handle, without adjustments, and were indeed designed to cope with since E15 is being pushed in some areas (and higher percentages) but this would definitely require changes to nearly all existing engines. E85 (and E70) are only for special Flex Fuel vehicles, on which the engine management system can determine what fuel is being consumed. Flex-fuel vehicles can run on any mix from E0 to E85, and need to as E85 changes to match the seasons E85 in summer and E70 in winter, depending on climate. Flex fuel vehicles have only recently started to appear in Australia, but have been available in Brazil and the USA for several years. It will be some time (if ever) before boats are available for E85. Flex fuel vehicles require more complex management systems with wide range exhaust gas oxygen sensors, which are difficult to keep working in the presence of water, especially sea water. And the fuel range will be about 30% less on E85. Fuels are a mix of HC compounds in order to give desirable cold starting, hot starting, driveability and economy characteristics. This is varied (often weekly) from winter to summer. These lines show how the Winter fuels (lower line) vapoursise at lower temperatures for better cold starting and mixing with cold air. Ethanol (by itself) has a lower vapour pressure than petrol, but when added to petrol the mix has a higher vapour pressure than petrol. E10 is not just petrol with Ethanol, but must be formulated to cater for the changes that adding Ethanol makes. It therefore follows that losing some, or all, of the ethanol (from evaporation or phase separation) does not leave behind normal petrol.

6 Fuel system components from 1985 and prior were NOT designed for E10, so should not be used. This sketch lists the materials that required change for Ethanol fuels, just about everything. All plastic and rubber parts and even the coatings on steel tanks! E10 can hold up to about 0.5% water, in suspension, which makes it electrically conductive and therefore corrosion is more likely in Ethanol fuels. Ethanol is also a better solvent than Petrol, so gum and varnish deposits that petrol did not shift can be liberated by E10, clogging filters. The biggest problem is likely to be phase separation. Fuel and water do not mix, but E10 fuel and water will, up to a very small percentage. When that percentage is exceeded, the water joins forces with the ethanol and they both separate from the petrol to form a separate layer at the bottom of the fuel tank. The blue line shows the phase separation point for E10 at various temperatures between freezing and 40C. The maximum amount of water is between 0.4 and 0.6L And it s quite temperature dependant. Half a litre of water in a 100 litre tank of E10 on a nice warm 25C day is no problem. The water will be invisible, mixed with the fuel. But if the temperature drops to 10C (below the line in the graph), and we agitate the tank, phase separation will now occur. The causes a new layer to form at the bottom of the tank and in this example it will be nearly 10L of just water and ethanol. Because the engine s fuel pick up will be near the bottom of the tank, once phase separation occurs that is all the engine will get. And it won t run very well, if at all, on an Ethanol/Water mix. The potential for fuel system damage from phase separation is high. Here s an example, and a method of testing if you have Ethanol fuel or not. Put 20ml of water in the bottom of a 100ml graduated flash. Now add 80 mls of E10, cap and shake. Allow to stand for several minutes until the lower layer is stable. Note the increase in the lower level, in this case 6ml. Divide this increase by the original fuel quantity (80ml), then multiply by 100 to get percentage. Most, but not all of the ethanol will join forces with the water, (if there s enough water for phase separation and correct temperature), with some agitation. This test shows 8% of the original fuel is now joined together with the water, in a separate layer.

7 Given the potential for problems, here s what outboard engine manufacturers are recommending First - What NOT to do 1 Don t leave the tank nearly empty, allowing plenty of room for the tank to breath each time the temperatures goes up and down (daily), pulling in warm, moist air. 2 This also leaves plenty of exposed tank walls on which condensation can form, then drain to bottom of the tank. 3 Having very little fuel means you get enough water to reach phase separation quantity very quickly. What you should do 1 Fill the tank to increase the amount water required before phase separation, reduce the breathing area of the tank and reduce exposed wall area where condensation can form. 2 Add a fuel conditioner that will increase the amount of water it can hold, reduce oxidation and loss of the more volatile compounds. Must be added to fresh fuel, a conditioner can t fix old fuel. 3 Use a good large water separating filter, and remember if you get visible water in the filter when using E10, phase separation has ALREADY occurred, so your octane may be too low. Engine maintenance also plays a part with ethanol fuels and especially so on modern emission controlled engines. Of course the usual maintenance items apply, spark plugs, oils, filters and so on, but one area that is very important for maintaining good emissions and combating carbon deposits is engine temperatures. This is the typical temperature graph for an Evinrude E-TEC. At low speeds we want the engine to be hot, up between 60 and 80C. Right up close to the upper limit possible with salt water. This is because good fuel vaporisation, low emissions and low deposits are highly dependent on correct engine temperature. At higher speeds (above 2000 rpm) there is sufficient air turbulence and in-cylinder temperature for good atomisation, so here we will reduce the cooling system temperature to 40-60C for a denser inlet charge and higher power and torque output.

8 Evinrude, like most engine manufacturers, provides branded products for maintenance. 2+4 Fuel Conditioner reduces the fuels tendency to oxidise (react with the air in storage), increases its ability to hold water in suspension and reduces the catalytic effect of any metals in the fuel system. Some metals (such as copper) can cause petrol to oxidise much faster than when there are no metals in contact with the fuel. Carbon Guard is a detergent product intended for regular use by adding it to the fuel. It will reduce the formation of carbon on piston and combustion chamber surfaces. For boaters who spend a lot of time at low speeds (which is most of us) it s a very worthwhile additive, because this when deposits are most likely to form. Engine Tuner is an aggressive carbon remover for use during routine servicing, but not while using the engine. Also new since we ve implemented a quick-rise inductive ignition system for all E-TEC models. This new system provides more consistent combustion and less plug wear, resulting in a smoother-running engine, improved fuel economy and longer spark plug life. As the graphic shows some of the electronics are now inside the coil, so it s a completely new and larger coil for each cylinder. Since the 1970 s outboard ignition systems have been CD (Capacitor Discharge) because it s very quick rise time prevents plug fouling. CD systems give a very quick but very brief spark. That was OK when there was too much fuel in the chamber, but not today. With low emissions engines we run the mixture quite lean and stratified at low speeds. To ensure always lighting the fuel mix, on low emission engines CD systems used a multi-strike system is used. That is, for every firing cycle the spark plug is fired several times (3 to 8), to ensure we always light the fire. Other types of engines use an inductive system, but they take a long time to charge which is unacceptable for outboard applications, but they do have a long spark duration. The best of both worlds is fast rise time with a long duration and this is what the IDI system features. Evinrude s new IDI system has a quick charge and long duration that creates better starts, smoother running and far less wear and tear on your spark plugs