Outboard Technologies - Part 1

Outboard Motor Technologies Compared and Contrasted

Back in the �good old days� almost all outboard motors were simple carburetted 2-strokes that had to have their petrol pre-mixed with oil at a ratio of 25:1. They drank fuel, fouled spark plugs and dropped a wee bit of fuel and oil into the water every time we tilted them. And of course, being carburetted 2-strokes, around 25% of the petrol/oil mix went straight out the exhaust and into the water, the petrol quickly bubbling up and evaporating into the air, the oil remaining as a thin slick on the surface. Back then, very few people gave a thought to the environment. Since then, environmentalism has matured into a powerful political force. So much so that environmentalists have been successful in having legislation enacted in the USA and the EU that has wrought a revolution in outboard motor technologies as manufacturers worked hard to develop outboards that would meet the new emissions standards, and boaters wanting to buy a new outboard today have a bewildering array of competing technologies to choose from. NZ Propeller�s Technical Editor, Peter J. Morgan, offers this illuminating look that may just help you to make up your mind as to which new technology you want to go to sea with. In this issue, Part 1 deals with 2-strokes, and in the next issue, Part 2 will deal with 4-strokes and peek into the future to give you an idea as to what further developments may be on the way.

In order to understand the rationale for the technological changes that have occurred, one first needs to understand the technology as it was in times gone by. Why do simple carburetted 2-strokes dump about a quarter of their fuel/oil mix straight out their exhaust ports? A carburetted 2-stroke engine is simpler, lighter and cheaper to manufacture than a 4-stroke. There are no camshafts or poppet valves. Fuel is fed into the carburettor through a simple needle valve where it is mixed with air and enters the crankcase in response to a drop in pressure as the piston travels along the cylinder, compressing the previous charge of fuel/oil/air mix towards the cylinder head (let�s call this the first stroke). The spark plug fires, igniting the fuel/oil mix, driving the piston back along the cylinder (the second stroke, at the end of which, the piston has driven the crankshaft around one revolution � hence the descriptive name, 2-stroke). As the piston travels along the cylinder, it uncovers openings (ports) in the cylinder wall � firstly a group of ports for the exhaust to flow out, and secondly another group of ports (usually on the opposite side of the cylinder wall), for the fresh intake charge of fuel/oil/air mix to flow into the cylinder after having been compressed in the crankcase. Unfortunately, it�s just not possible to arrange for these two groups of ports to be far enough apart along the length of the cylinder wall, and at the same time be large enough, for the exhaust port to be closed off by the piston before it uncovers the intake ports, so quite a bit of the fresh intake charge goes straight out the exhaust ports, unburned. Hang on a minute, how could the pressure in the crankcase increase when the carburettor throat is open? Because between the carburettor and the crankcase is a simple reed or flutter valve, which opens when the pressure in the crankcase is lower than the pressure in the carburettor throat, and closes when the pressure in the crankcase is higher than the pressure in the carburettor throat. Thus a carburetted 2-stroke acts as a simple pump to self-induct its own fuel/oil/air mix. These are really simple engines, and engineers spent years �tweaking� their designs, gradually making them better and better, improving the �scavenging� of the exhaust gases out of the cylinder, whilst allowing less and less of the fresh intake charge to escape unburned out the exhaust, and developing better and better oils and spark plugs, to practically eliminate fouling, to the point where they became extremely reliable and just about indestructible.
With the advent of strict emissions limits in the USA and EU, due to take a more demanding step in 2006, and the California Air Resources Board (CARB) having even stricter regulations due to take effect in 2008, it quickly became apparent that simple carburetted 2-strokes would go the way of the dinosaur. Manufacturers of 4-stroke outboards realised that with the addition of electronic fuel injection, a technology already developed and proven for car engines, they could just squeak in under the new CARB 3-Star limits, without having to resort to automotive-style catalytic converters.
Meantime, two engineers � a young Australian in Perth and a young East German, independently had inspirations as to how to fix the 2-stroke�s problem. Easy, really, all you have to do is come up with a way to get the fuel into the combustion chamber in such a way that NONE of it can get out the exhaust ports BEFORE firing the spark plug!
Ralph Sarich in Perth had invented an �orbital� engine, which he was trying to get off the ground. As part of his new design, he had invented a way of finely atomising petrol by squirting a blast of 550kPa (80psi) compressed air across the spray from an electronic fuel injector, and had successfully tested his fuel/air direct injection system on a converted Suzuki 3-cylinder 2-stroke engine. He was able to get his engine running on a �stratified charge� at low speeds � this means that at low speeds it has enhanced fuel economy, running a much leaner mix of fuel and air. He called this new technology the Orbital system, although it had nothing to do with his �Orbital� engine. In the 1990s he licensed a number of companies, including, OMC (the then makers of Johnson and Evinrude outboards) Mercury Marine, Tohatsu, Bombardier Recreational Products (BRP) (for its Rotax engine line), General Motors, Mercedes, Ford, Fiat, and Piaggio V.E.S.p.A, to utilise and further develop his ideas. Mercury, Tohatsu and BRP have commercialised the technology � the Mercury brand name being OptiMax. The engines necessarily have a separate, belt-driven air compressor.
The young East German engineer came up with an idea for a new-fangled electronically controlled solenoid-actuated injector to enable high pressure direct injection of 2-strokes, eliminating the carburettor, and also eliminating the wastage of unburned fuel. His concept used a solenoid valve to pressurise fuel within itself to finely atomise the fuel, needing neither an air compressor nor a high-pressure injector pump. He went to a West German engineering firm where the directors liked his idea, and Ficht direct injected 2-strokes were developed. The senior engineers of OMC, manufacturers of Johnson and Evinrude outboards in the USA at that time, learned about this new technology and soon OMC was a licensee, to put Ficht technology into OMC outboards, in preference to Sarich�s Orbital technology. Only the engineers closely involved at the time will know what really happened, but I suspect that the development was costing more money than OMC�s finance people wanted to spend, and intense pressure was brought to bear on the engineers, with the result that the Ficht technology was released to the market before the development program had quite finished. Some time after the introduction, some of the Ficht motors gave trouble, burning holes in their pistons. Whatever, OMC was in such a vulnerable financial position that when sales dropped dramatically, through the resulting adverse publicity, the company became insolvent and went out of business.
Meantime, Yamaha�s engineers were developing their own type of high pressure direct injection 2-strokes, which they called, not surprisingly their HPDI system. In 1999, this was �last to market� amongst direct injection technologies, and probably as a result of bearing in mind what had happened to OMC, the HPDI system did not, and still does not, feature lean-burn �stratified charge� technology.
In 2001, realising the value in the Johnson and Evinrude brands, and confident that it had the financial resources and that its engineers had the talent, enthusiasm and drive to fix and further develop 2-stroke direct-injection technology, Bombardier bought the major assets of OMC, under its Bombardier Recreational Products (BRP) wing, which was already a highly successful manufacturer of snowmobiles and personal watercraft. Bombardier, a highly successful manufacturer of aircraft, trains, transportation and spacecraft equipment, was no stranger to buying companies in trouble and successfully turning them around, having bought and resurrected an ailing Lear Jet Corp. Since then, BRP has been separated off from Bombardier, and is now quite independent.
George Broughton, director of the Engineering, Boats and Outboard Engines Division of Bombardier Recreational Products, in Sturtevant, Wisconsin, USA, and his team of engineers quickly went to work taking the bugs out of the Ficht system, developing and incorporating their own ideas as they went. In a clever marketing ploy, BRP kept the Johnson brand as carburetted 2-strokes and gradually introduced 4-strokes sourced from another manufacturer. BRP re-launched the re-vamped Evinrude Ficht Ram outboards and set about clawing back their market share �one customer at a time�. The engineers didn�t stop, however. They had learned so much about outboards while �fixing the Ficht�, particularly with regard to the operation of the electronic fuel injectors, that they went to BRP�s directors, most likely saying �We can do much better than that�. As a result, they were given the go-ahead to develop and manufacture a new line of Evinrudes, to be branded as E-TECs, at the heart of which is BRP�s own quite revolutionary fuel injector.

Fuel Injection
The fundamental difference between E-TEC fuel injectors and what are now considered conventional electronic fuel injectors as used in cars and trucks, 4-stroke EFI outboards, Mercury OptiMax, Yamaha HPDI and Tohatsu TLDI direct-injected 2-stroke outboards, is that all except the E-TEC need a high-pressure fuel pump and piping (rail) system to deliver high-pressure fuel to the injectors. For all except the E-TEC, the injector merely acts as a metering device, and the amount of fuel delivered is controlled by each engine�s computer determining when, and for how long, to open the injector, with the fuel being backed up behind the injector in a high pressure rail, supplied by a separate high-pressure fuel pump.
In contrast, the E-TEC injector is unique in generating its injection pressure within itself, whilst being fed by ordinary low-pressure (200kPa (30psi)) fuel lines by the same old reliable water cooled electric fuel pump that is an integral part of the water separator that has served in Evinrudes and Johnsons for more than a decade. Thus the E-TEC, alone among high-tech outboards, has no belts or chains driving pumps, camshafts, alternators, compressors or superchargers.
All other things being equal, the higher the injection pressure, the better the atomisation, the more efficient the combustion and the lower the emissions. Whilst Yamaha claims the highest injection pressure, 6.9MPa (1000psi) � but only on the 250hp and 300hp models, the 150, 175 and 200hp models having an injection pressure the same as the E-TECs�, at 4.8MPa (700psi), one exception to this generalisation is the air-injection system as used in the OptiMax and Tohatsu TLDI. Another exception is the patented swirl nozzle in the E-TEC injector, which is claimed by BRP to make combustion even more efficient than that achieved by Yamaha�s HPDI 250hp and 300hp models, even though its injection pressure is 4.8MPa (700psi). The swirl-nozzle fuel injector has 1.17mm wide tangential slots that cause the fuel droplets to swirl around as they enter the combustion chamber. The nozzle is manufactured by metal injection moulding.

Fuel is re-circulated through E-TEC injectors continuously to cool them and ensure any air or vapour is removed. This is because all injection systems can only accurately meter liquid fuel. Any air or vapour must therefore be removed. The E-TEC injector, like the Ficht one before it, uses an electro-magnet, but whereas the Ficht injector had a fixed electrical coil, a moving heavy steel armature, and a helical coil return spring, the E-TEC injector uses a Lorentz coil, in much the same way as a conventional loudspeaker. The E-TEC injector�s lightweight moving coil bobbin has much lower inertia than the Ficht�s heavy steel armature, enabling it to be accelerated and decelerated much more easily and more quickly.
Inside the coil are two fixed, powerful rare earth permanent magnets. When current in the coil is switched on, the electro-magnetic field reacts with the permanent magnets, causing the coil bobbin to move with great force. The coil bobbin pushes the plunger, and for the first 0.5mm or so it moves freely through the fuel, until it contacts the poppet valve. Now the plunger and poppet valve form a piston and any further movement pressurises the fuel behind the nozzle. forcing it open and spraying fuel into the cylinder as very fine droplets. When sufficient fuel has been injected, as pre-determined by the engine�s electronic control module, the current is turned off in the coil and a very brief reverse polarity pulse is sent. This very quickly stops the bobbin and plunger, and starts it returning in time for the next injection event.
A second very brief reverse polarity pulse is also sent when the coil is almost fully back, to stabilise it and ensure a �soft� landing, preventing it from bouncing. The use of a lightweight moving coil system and electrical pulses to control movement in both directions is how the E-TEC injector can be both more powerful and faster than previous designs. Compared with the Ficht injector, the E-TEC injector is smaller, lighter, has 25% fewer total parts and 50% fewer parts with critical tolerances.
An E-TEC engine will start within one revolution, even after being in storage over winter, something most two-stroke owners will find hard to believe. In any fuel tank there is almost always an air space above the fuel and therefore oxidation may occur over time. Carburettors drain themselves over time, so it is often difficult to start a carburetted 2-stroke that has sat unused for a while. In an E-TEC, each injector remains full of fuel, and no air can get near it, so the fuel stays fresh.
The following comparison highlights why the E-TEC injector is so superior to the Ficht injector:

Ficht�E-TEC
Maximum power per cylinder�45 hp�80 hp
Maximum engine speed�7500 rpm�10000 rpm
Injection time�0.005 s�0.0025 s
Maximum injection pressure�3.1 MPa�4.8 MPa

All E-TEC outboards carry the CARB three-star rating. To achieve this ultra-low emissions rating for a 2-stroke it is necessary to incorporate a lean-burn, �stratified charge� combustion mode at low engine speeds. Up to about 2000 rpm, the fuel spray is concentrated toward the tip of the spark plug, hence the term �stratified charge�. This small volume of combustible mixture is ignited, and the flame then expands to the leaner areas of the combustion chamber. Stratified charge technology is the reason behind the excellent low-speed fuel economy figures of both the E-TEC and the OptiMax direct-injected two-strokes, and their ultra-low emissions. In developing its HPDI technology, Yamaha opted not to incorporate a stratified charge mode, and this is why the HPDI cannot match the low-speed fuel economy of E-TEC and OptiMax engines, and has not achieved the CARB 3-star rating. Incidentally, none of the 4-stroke outboards can match the low-speed fuel economy of the E-TEC and OptiMax, and they won�t until they too incorporate direct injection (DI) technology, which is the only known way to consistently achieve and maintain a stratified charge (lean burn) mode. DI is still rare in petrol powered cars. It is used by Mitsubishi, and then only in some (GDI � gasoline direct injection) models, and Toyota has some models featuring this technology, including one or two Lexus models sold in New Zealand.
A successful application of lean-burn technology requires sophisticated sensors and electronics. A lean mixture burns very hot, and as engine load and speed increase under lean-burn conditions, the pistons get increasingly hotter. If piston temperatures rise too high for the aluminium alloy from which they are made, they can melt, and cylinder-wall scoring follows, compounding the damage. Both the E-TEC and OptiMax systems therefore have sensors that closely monitor the cylinder head temperatures. These are linked to the EMM, which adjusts the fuel/air mix accordingly, with the result that at engine speeds above about 2000 rpm the mixture is enriched to the point where the engine is no longer operating in lean-burn mode. In addition, E-TEC outboards have thermostatically controlled high-flow cooling systems, designed to keep the cylinder heads and walls from overheating. As an added precaution, E-TEC pistons are manufactured from a new metal alloy, developed by Nasa for the space program. This allows them to operate in lean-burn mode at considerably higher temperatures than older-technology pistons could cope with. Rest assured that developments are underway in materials technology for ceramic pistons to be introduced. An interim step will probably be a ceramic coating on the Nasa-alloy pistons � interested readers may wish to check out the website www.keronite.com
The OptiMax ECM controls the electronic oil pump, and monitors and adjusts engine functions for atmospheric pressure, altitude and ambient temperature in addition to cylinder head temperature, throttle position, and engine speed. The precision control of the ECM allows OptiMax engines to idle at just 550 rpm, meaning great control and manoeuvrability in docking and other tight situations, as well as snail-like trolling speeds.
In an interesting turn of events, recently BRP announced that it had sold the manufacturing rights, but not the intellectual property, to its E-TEC fuel injectors, to Orbital Corp, the company founded by Ralph Sarich.

Fuel pump and vapour separator
The E-TEC vapour separator with integral low-pressure electric fuel pump is basically the same well proven water cooled unit as that used on the V4 and V6 DI models, dating from the 1990s. The vapour separator is a fully pressurised design that captures and separates any vapour present in the fuel, then releases the vapour only when the internal liquid fuel level drops. This ensures there are no vapour emissions until the engine is running, when any trapped vapour is then vented into the intake manifold where it is consumed during combustion. The vapour separator is also water cooled to remove excess heat from the fuel, especially at low speeds when very little fuel is consumed and most of the fuel is being re-circulated between the injectors and the vapour separator.
The Yamaha HPDI motors use two fuel pumps in tandem � a conventional low-pressure 12V electrical fuel pump feeding a high-pressure mechanical pump that is driven off the crankshaft by a toothed belt. The injection pressure is 4.8MPa (700psi) for the 150hp, 175hp and 200hp models, and 6.9MPa (1000psi) for the 250hp and 300hp models. The 250hp and 300hp models have twin high-pressure pumps, one feeding each cylinder bank.

The OptiMax system uses a mechanical air compressor that is driven off the crankshaft by a serpentine belt to feed air regulated at 550kPa (80psi) to the split air/fuel rail. The electric fuel pump supplies fuel from the Vapour Separating Tank (VST) to the same rail but at 620kPa (90psi), this is then sprayed from the fuel injectors through the air blast from the air injectors into the cylinder, finely atomising it for highly efficient combustion. The air and fuel injectors are fired at the same time. The air fuel rails have fuel and air regulators to keep the fuel pressure at a constant 70kPa above the air pressure.

Ignition
When the key of a V6 OptiMax is turned to the run position, electrical energy is available to the ECM, fuel pump, coils and injectors. These components are now energised but lie waiting until the crank sensor tells the ECM that the engine has reached a pre-programmed rpm. The crank sensor measures where the engine is in its cycle and the engine�s speed by counting the teeth on the flywheel. In turn, the ECM takes this signal from the crank sensor and tells the "coil drivers" to start working, and in turn the coil drivers tell the coils to make the spark which is sent into the cylinder via an HT lead and spark plug.
The Yamaha HPDI uses the same transistor controlled ignition (TCI) system as Yamaha�s 4-strokes � a thoroughly proven, very reliable system.
The E-TEC�s ignition system is unique amongst modern outboards in running off a magneto � like a Model T Ford had in the early 20th century. BRP says that this is for a simple reason: many recreational vehicles, including boats, are put into storage at the end of each season, and then pulled out when the weather turns favourable. Batteries die in storage, so relying on one to drive the fuel injection system and engine controller only adds to owner frustration. The E-TEC magneto, which is built-in to the flywheel, produces from 150 to 300 volts, which is reduced to 55 volts to drive the oil and fuel pumps and the fuel injectors. It is further reduced to 14.7 volts to charge the battery, if the boat has one. It is noteworthy that the 25hp Mercury Thunderbolt, the world�s first 4-cyl. in-line outboard, had magneto ignition. My dad had one in 1948 � the only one to come to NZ. It had a rope-start system, around the exposed chromed steel flywheel, and had no recoil starter and no battery. It had no forward, neutral and reverse gears, either � just forward, and that meant it had to be started in gear, and from cold it sometimes needed quite a bit of throttle to get it to fire! I well remember that my big brother, who was 12 at the time, could start it, and the pair of us roamed freely in the Bay of Islands that first summer. I pleaded with my dad to be allowed to run it on my own, just as my big brother did. My dad said that when I was strong enough to consistently start it, then I could run it on my own. Four years later, when I was 12, I too was strong enough! We had that thing for 10 years! In a practical sense, it is simply not possible for a person of average strength to rope-start a 2-stroke of more than about 90hp.
E-TEC engines are designed to start within one revolution, something most two-stroke owners will find hard to believe, especially for an engine that�s been in storage. The explanation is in the sealed injection system. Though the fuel in the gas tank may oxidize over time, no air can enter the fuel system itself, so the fuel in the line stays fresh. As the flywheel starts to turn, the magneto sends current to the engine controller, which determines where the piston is, when to inject the fuel and when to fire the spark plug � all this being done in less than one revolution.

Lubrication
In direct injected 2-stroke engines, oil is drawn in from the bottom of the cylinder, but fuel is injected from the top. Since the fuel and oil don't mix, the oil isn't thinned sufficiently to move up and lubricate the top piston ring. That's a recipe for engine disaster � as one manufacturer has discovered.
Yamaha's HPDI system solves this problem with a new, patented bottom piston ring that's made with a taper every 30 degrees, for oil bypass. The 12 tapered areas around the ring are designed to allow sufficient oil to reach and lubricate the top ring.
The lubrication system on OptiMax features an electrically driven oil pump, and multipoint delivery, all controlled by the ECM. Oil is delivered directly through the reed plate to the crankcase and also directly to the connecting rods. Also, a small amount of oil is injected into the air entering the compressor, as it too must be lubricated. Oil ratios range from a miserly 1:400 at idle to 1:44 at wide open throttle. Assuming an average oil ratio of 1:100 for an OptiMax and the average boater doing 50 hours a year, and assuming an average fuel consumption of 35 litres per hour, that�s 17.5 litres of oil a year.
The six-cylinder Verado 4-strokes hold 8 litres of oil, which must be changed after the first 20 hours and thereafter every 100 hours or at the end of each year�s operation, whichever comes first. Based on the average boater doing 50 hours a year, and assuming an average fuel consumption of 35 litres per hour and no top-ups being needed, this equates to an oil consumption of 1 litre per 219 litres of fuel, just under half what an OptiMax would use � not a very significant saving, especially given that fuel costs represent only 10%-15% of the total cost of owning a trailerboat.
The OptiMax and Tohatsu TLDI have a separate air compressor driven from the engine, by a belt and pulley arrangement. This robs some horsepower from the engine, requires more energy from the battery and also generates some noise. The compressor output is 550kPa (80psi) air that is distributed in a pressure rail or hose to each cylinder�s air injector, and it is this air being injected as a spray across the spray from the fuel injector that causes the fuel to be finely atomised � essential for efficient combustion. There is therefore considerably more plumbing under the cowling of OptiMax and Tohatsu TLDI engines than on E-TEC and HPDI engines. The fact that OptiMax has twice as many injectors as E-TEC and HPDI also considerably increases the electrical load. Also, in the OptiMax and TLDI, fuel pressure is raised to 620kPa (90psi) by an electrical fuel pump. OptiMax and Tohatsu TLDI engines are therefore very high consumers of electrical energy and often do not produce net charging current until running at a fast idle. The foregoing is why OptiMax and Tohatsu TLDI engines have strict requirements for battery capacity so that they can run at low idle speeds for a decent period of time.
E-TEC owners have the option of running their engines on E-TEC synthetic oil, and can have their engines� EMM re-programmed by their dealer to use half as much oil. There�s no cost saving, though, as the synthetic oil is about twice the price of mineral oil. The real pay-off is that there�s even less smoke produced.

Oil and Catalysts
If and when pollution regulations get tougher, will direct injection 2-strokes be at a disadvantage because they have a continuous-loss oil lubrication system, in contrast with the sump systems used in 4-strokes? The answer has to be �no�, because the amount of oil burned is about 1% of the total intake charge, and it does not mix with the petrol. The average user of a 50-hp direct-injected 2-stroke will go through about 2 litres of oil per year, and that will get spread over a huge amount of water and air! Hydrocarbons are the predominant pollutant, a portion of which are scavenged and burned in the next combustion cycle. If and when emission standards get tougher, BRP says that a simple 1970�s technology reduction catalyst is available to be brought into service again, so at least one manufacturer of 2-strokes is confident of their continuing future. In its marketing, BRP keeps asking the question �Can you be sure that the used oil from your 4-stroke outboard has been disposed of properly, according to the best environmental practices? In many instances, in this country at least (and never mind the rest of the world), the answer has to be �Yeah right!�
Pollution Comparison
So overall, how do direct-injected 2-strokes compare with 4-strokes in their exhaust pollutants? The answer is that they compare exceedingly well. So well that in fact BRP was the first � and remains the only � outboard manufacturer to be given a �Clean Air Excellence Award� by the USA�s Environmental Protection Agency (EPA), for its E-TEC line of outboards.
A fact not widely known is that neither the EPA nor the CARB, nor even the EU, have yet begun to regulate the emissions of carbon monoxide, which is far more harmful to human health than the pollutants that are currently regulated, namely nitrous oxides and sulphur dioxide. A fact also not widely known is that direct-injected 2-strokes emit much lower levels of deadly carbon monoxide than do 4-strokes. This is particularly relevant to those travelling in increasingly popular hardtops, where the �station wagon effect� causes exhaust gases to eddy around and get sucked back into the wheelhouse.
Finally, is all this high technology worth it for the average boater? On a strictly cost accounting basis, do the fuel and oil savings justify the extra cost of the outboards compared with old-technology carburetted 2-strokes. The answers, respectively, are in my humble opinion �Maybe (depending on each individual boater�s disposable income)� and �No, definitely not!� But �pleasure� boating has got very little to do with cost accounting. Putting it simply, the main reason that �pleasure� boaters in their droves are preferring the new high-tech outboards over the old-technology non-DFI 2-strokes is that the new motors are very much more �pleasurable� to use � end of (Part 1) story!

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