Will Fuel-Injection Improve Engine Performance at High Elevations

Optimizing the performance of Boston Whaler boats
Pogiepika
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Will Fuel-Injection Improve Engine Performance at High Elevations

Postby Pogiepika » Thu Jan 28, 2021 1:17 pm

I plan to buy a four-stroke-power-cycle engine with fuel-injection and use it at altitudes that range from sea level to 9,500-feet.

Does fuel-injection as used in a HONDA or TOHATSU 40-HP or 50-HP engine produce a benefit for high-altitude performance?

jimh
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Re: Will Fuel-Injection Improve Engine Performance at High Elevations

Postby jimh » Thu Jan 28, 2021 1:28 pm

Use of electrically controlled fuel-injection as seen in modern marine smaller outboard engines like a HONDA or TOHATSU 40-HP or 50-HP is very common. But the metering of fuel into the engine intake air stream with an electrically controlled fuel injector does not inherently mean that the engine will adapt to radical changes in altitude.

Some modern engines include a barometric sensor and an intake air temperature sensor. This sensor data is provided to the engine management module (EMM) or engine control unit (ECU). The EMM or ECU may then use this data to alter the amount of fuel that will be dispensed so that the ratio of fuel and air remains in the desired proportions. That sort of sophistication in fuel-air mixing control is provided by the engine designers and incorporated into the EMM or ECU. It does not reside in the fuel-injectors themselves.

Generally as the elevation increases the air becomes less dense. Unless the engine uses an air intake boost method, such as supercharging or turbocharging, there is no way to increase the intake air volume to make up for the lower density. Note that in older carburetor two-stroke-power-cycle engines there is, actually, a pumping mechanism in the design that pushes air into the combustion chamber, so a classic two-stroke-power-cycle engine has some effect of boosted intake air pressure. But a four-stroke-power-cycle engine with the typical intake and exhaust valve arrangements does have any boost method.

Modern automobile engines use a Mass-Air-Flow sensor to determine the amount of air flowing into the engine. I am not aware if that technique is used on any small-horsepower marine outboard engine. See

https://en.wikipedia.org/wiki/Mass_flow_sensor

I don't have an authoritative cite, but several boaters have commented that a mass-air-flow sensor is not permitted on a boat engine because of the heating element in the sensor.

A Manifold-Air-Pressure (MAP) sensor may be used. See

https://en.wikipedia.org/wiki/MAP_sensor

In general, the purpose of adjusting the amount of fuel to match the air density is to keep the fuel-air mixture at the proper ratio. This permits the engine to run smoothly, as otherwise with increasing altitude the fuel-air ratio may become too rich and result in poor engine run characteristics.

But maintaining the proper fuel-air mix ratio as the density of the air decreases does not preserve power output. With less fuel being burned in the combustion chamber, the engine will develop less power.

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Phil T
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Re: Will Fuel-Injection Improve Engine Performance at High Elevations

Postby Phil T » Thu Jan 28, 2021 1:33 pm

If you will be running the engine at 9500 ft elevation, you will loose horsepower regardless of EFI.

HP Loss = (elevation divided by 1000) X (0.03 x rated horsepower)

A 40hp at sea level will be a 28.6hp at elevation.
A 50hp at sea level will be a 35.7hp at elevation.
A 60hp at sea level will be a 42.9hp at elevation.
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jimh
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Re: Will Fuel-Injection Improve Engine Performance at High Elevations

Postby jimh » Fri Jan 29, 2021 1:02 pm

Another confusing term is the use of "injector" with regard to the electrical fuel metering system. On many engines, the so-called "injectors" are simply gate valves that open and close on an electrical signal. There is no pumping or injection motion, and the flow of fuel is created by an increased fuel pressure in the supply of fuel to the metering device via a fuel manifold system. The fuel manifold system tries to maintain a constant fuel pressure at each fuel "injector" so that the amount of fuel being metered will vary primarily on the amount of time the gate valve is open.

When the electrically controlled gate valve opens, fuel flows through the valve into the air stream that is flowing into the combustion chamber. The air pressure in this air stream is often at atmospheric pressure or below, due to the suction effect of the piston in the cylinder in a four-stroke-power-cycle engine being on a downward or intake stroke. The fuel moves into the air stream not because it is being "injected" into the air stream, but because it is under pressure and the air stream is also sucking in the fuel.

The electrical fuel gate valves are controlled by various electrical devices with various amounts of sophistication. These devices are the "electronics" of the fuel metering system.

In more modern internal combustion gasoline fuel engines there are actual fuel injectors that pump or force the fuel directly into the combustion chamber with very high pressure created in the injector itself. These direct-injectors will be able to push fuel into the cylinder even as the internal pressure in the combustion chamber is rising during the piston compression stroke upwards. Or, in some instances, the injector fuel manifold system is maintained at a very high pressure.

In more modern internal combustion gasoline fuel engines the electronic controller adjusting fuel flow to the electrically-operated fuel devices will use inputs from many sensors to determine the required amount of fuel to be added for proper combustion, generally using a stored mapping of fuel as function of multiple variables, and adjusting in real time to produce the best combustion.

Again, whether or not a particular engine contains real fuel injectors or employs sophisticated electronic control over them based on multiple sensor input cannot be inferred simply by the marketing of an engine as having "EFI."

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Re: Will Fuel-Injection Improve Engine Performance at High Elevations

Postby jimh » Tue Feb 02, 2021 10:21 am

Please note that this thread is ONLY discussing the topic of how use of fuel injection might improve engine performance at high elevations.

This thread is NOT discussion a particular boat, a particular engine, or what factors should be considered in choosing an engine for re-power.

If there is a particular boat and a particular engine that is being contemplated for repowering that boat, START A NEW THREAD about those topic.

Any further comments not related to how use of fuel injection might improve engine performance at high elevations will be deleted from this thread.