Fuel efficiency, cost and ethanol

Fuel for debate

Rising fuel prices and greenhouse gas emissions seem to be the two most popular story ideas seen in today's media. Both subjects affect boating enthusiasts and scrutiny of these matters by the relevant authorities is constantly in progress.

New emissions regulations are coming and companies innovate to stay ahead of the regulators. Even if you don't care about emissions directly, technological advances in engine design are still of interest because one major aspect of reduced emissions is reduced fuel consumption - and that's a direct hip pocket issue for almost anyone who owns a boat.

Boat and engine tests that quantify things like fuel consumption make extremely popular reading, which is why we run them, though the range of similar subjects in magazines and on the web can be difficult to assemble and analyse. However, we recently saw the Mercury Fuel Cost Calculator, which takes some of this data and puts it into an easy to access format that you can use to determine how much it's going to cost to run an engine you might be considering. Not only is this extremely timely, it's very easy to use.

INDICATOR RATHER THAN COMPARITOR
Although the cost calculator has been made available by Mercury, models from all manufacturers are included.

The data comes from the comprehensive archives of BoatTEST.com rather than Mercury itself. There are 33 engines listed, so obviously they weren't all tested side-by-side under identical conditions. Consequently, the calculator carries the caveat that it's not valid for direct comparison of various models from each of the manufacturers listed.

Still, it provides an excellent indication of what the fuel component of your total operating cost will be, so we visited Mercury to discuss the calculator and more.

"Like anyone, we're concerned about rising fuel costs," said David Meehan from Mercury, "We wanted to bring some perspective to the discussion."

He pointed out that most operators spend a great deal of time cruising at perhaps 3000 to 3500rpm.

Looking at the numbers in that range for, say, an OptiMax 90 two-stroke shows that with fuel at $1.75 per litre you'd spend around $18 and cover 37km in an hour. That's a fairly decent distance for not much money and compares very favourably with other leisure activities. Indeed, two rounds of mini-golf with my young daughter cost me $21 just the other day.

Ken Evans, Mercury outboard director, also sat in on the interview and suggested that dinner and a movie for an average family could cost a good deal more than three or four hours cruising in a boat at the above specified level. At those prices you wouldn't refrain from buying a boat because of the fuel cost.

So what happens to the numbers if fuel costs increase further? The calculator shows that even if fuel reaches $3 per litre, the cost per hour for the above configuration is still only about $30, which is still not that great compared with other leisure activities.

A recent article in The Australian by George Megalogenis and Teresa Ooi, was built upon research that suggested incomes have risen faster than fuel prices and that in real dollar terms, expenditure on petrol currently consumes a smaller portion of the family budget than it did 10 years ago.

The article also pointed out that some of the money previously spent on petrol (and some particular leisure activities) was now being spent in the home - interesting reading.

Patterns could be similar for boating enthusiasts except that money not spent on petrol for the family car would likely find its way into fuelling the family boat.

TIME FOR A CHANGE
In consideration of these things, and the general enthusiasm most boat owners have for being on the water, boating is likely to remain strong. Mind you, it's not just a shift in leisure spending that's going to support boating.

Older generation engines, particularly carburetted two-strokes, are gradually wearing out and being replaced. Re-powering an existing boat with a current generation engine will reduce the amount of fuel consumed enormously.

Ken pointed out that the latest OptiMax DFI (Direct Fuel Injected) engines can reduce fuel usage by as much as 45 per cent in some cases. So, if you've been putting fuel into an old two-stroke at current prices and it's become time for a new engine, you're about to reduce your fuel bill substantially.

The technology behind these savings is interesting, but to understand it properly we need to examine how fuel burns.

Combustion is actually a chemical reaction between gases - you can't burn liquid fuel. It has to evaporate before it can react with the oxygen molecules/atoms in the air. After it has evaporated, it must be mixed with air in the correct ratio in order to burn.

Yet even if both these conditions are met, gaseous fuel and oxygen still won't burn - not spontaneously, anyway. Some energy is needed to 'bump' the molecules into a reactive state and this is supplied by electrical energy bridging the gap in a sparkplug. Once mixture in the region of the spark begins burning, heat liberated by the process initiates a chain reaction that continues until all the fuel and/or oxygen has been consumed.

A cupful of fuel doesn't evaporate very quickly, but if you can divide it up into small enough droplets (atomisation), then the whole amount in the cup could evaporate extremely quickly.

It's all about the ratio of surface area to volume. The smaller the droplet, the greater it's surface area per unit of volume and the more rapidly it can absorb the heat needed to turn it into a gas in readiness for combustion.

Apart from delivering the correct amount of fuel to the combustion chamber, almost everything about a carburettor or fuel injector relates to atomising the fuel as effectively as possible.

Carburettors have done a pretty good job but suffer very definite limitations, particularly in some parts of the rev range. The carburetted two-stroke engine was extremely good at exposing those limitations which is part of the reason they have the reputation of being smoky in operation, especially at low revs when carburettor/engine efficiency is a long way from optimum.

INCREASING PRESSURE
Highly pressurised fuel squirted through small holes in the ends of injectors changed all that. Aside from delivering more precise amounts of fuel at all points in the rev range of an engine, electronic fuel injection creates even smaller fuel droplets, and does so at all points in the rev range. This is particularly beneficial at low revs when airspeed into an engine is low.

High pressure conventional EFI systems continue to serve well in many marine applications, but they aren't as well suited to two-stroke technology as they are to four-strokes.

The direct injection system, however, creates enormous benefits for engines of all types in all applications both on the road and water.

For those who don't know, the only thing that passes through the inlet tract and inlet port in this type of system is air. The fuel is injected directly into the combustion chamber - hence the name. There are variations on the theme among manufacturers and, in fact, we'll look at some other systems next issue.

Here, though, we're looking at fuel consumption based on the Mercury cost calculator so we'll describe the Mercury DFI system. We'll also concentrate on it because it's unique.

The Mercury DFI system is different in a couple of important ways. First, pressure in the fuel rail of a Mercury system is just 90psi. The reason a system with such low rail pressure can atomise fuel so effectively is because the fuel is first squirted into an injector chamber where it's combined with air pressurized at 80psi. Then, this mixture of pressurised fuel and air is injected directly into the combustion chamber.

Doing things this way creates the most finely atomised droplets of fuel possible. This maximises the use of each fuel charge resulting in better economy and lower emissions. Also, the way the fuel is added can be tailored to the prevailing conditions within the engine again optimising the use of the fuel.

As we mentioned, many engine manufacturers use direct injection but the air/fuel system described here is unique to Mercury.

KEEPING CONTROL
Utilising the full capabilities of a DFI system calls for sophisticated electronic engine management controls.

Mercury calls its engine management system a PCM and Ken points out that it monitors engine conditions on every stroke and determines how much fuel to inject based on readings of atmospheric conditions, engine speed and load. We'll talk more about direct injection next issue.

Other Mercury technologies contributing to fuel efficiency lie in the engine mechanicals.

In the Verado range for instance, lightweight but superior strength forged pistons are utilised because they take less energy to move than heavier cast types, and new cam profiles have also been introduced.

The oil feed grooves in the crankshaft main journal bearings have been shortened forcing more oil out through the sides of the bearings. This development alone reduced friction by three per cent.

Also, as a crankshaft spins at high speed it flings a great deal of oil about in the crankcase. Although it's just a liquid it still saps quite a bit of power at high speeds. To eliminate this Mercury extended and reshaped the sides of the crankcase oil dams to match the profile of the crank/rod assemblies more closely. This effectively traps oil that would otherwise be free to fly about in the crankcase.

In the earlier Generation I Verado the undersides of the pistons were oiled by pressure jets, but the power used to pressurise them was not insignificant. These have been deleted in the current Generation II Verado.

At the moment, Mercury engines feature three-star emissions compliance. But as we mentioned earlier, regulations are tightening. Four-star compliance is next (for sterndrives) and as a part of achieving it four-stroke engines in the range are going to be fitted with catalytic converters, which has been a difficult thing to do in marine applications.

As far as changes to direct injection engines are concerned to match four-star requirements, the company won't tell us anything. However, we can be sure that more stringent anti-pollution laws will likely lead to reduced fuel consumption. This can only help keep boating fuel costs down.

Meanwhile, if you're contemplating an engine upgrade, or maybe thinking about your first boat, check out the fuel cost calculator. We found a copy here

ETHANOL
We asked Mercury about how ethanol fits into the scheme of things in the company's development programme. Ken explained that all current generation Mercury engines and associated systems are designed to run on E10 (ten per cent ethanol) without a problem. However, this isn't the case with engines built before 1990. In these cases ethanol can corrode components significantly. And when the plastic and rubber components dissolve, they pass through your engine, which isn't good.

Further, when ethanol is mixed with petrol it doesn't evaporate, it reacts with some of the petrol to form a chemical that sinks to the bottom of the tank. At the top of the tank there's still a mix of petrol and ethanol, but between this layer and the bottom chemical layer, there's another layer called the ‘barrier layer' that's extremely corrosive and which can't be removed by any chemical means. This layering effect begins as soon as you fill your tank and the barrier layer will eat resin out of fibreglass and will also corrode aluminium.

Clearly, fuel tanks made from those materials, especially older tanks, will suffer. In fact, in America there's a class action going on against the oil companies for their failure to warn about this. These issues are less important in cars where fuel is used quickly, however boats can sit around for a long time over the colder months and this amplifies these problems.

Mass for mass, ethanol contains less energy than petrol, so more of it is required. It's been estimated for E10 fuels this equates to a 3.9 per cent power reduction. At a two-cent price difference Ken suggests that you're going backwards if you use it. He points out that E10 needs to be five to seven cents a litre cheaper than petrol to reach dollar parity. The situation is even worse if the ethanol content is higher as it is in the States with E85.