WHAT DOES AN ENGINE DYNAMOMETER DO?
Marine and automotive technicians are constantly required to fine-tune engines to ensure that they deliver optimal performance. Engines are crucial to the propulsion of any vehicle or marine vessel, and any issues will leave drivers frustrated and looking for a solution from an experienced technician. One of the many ways that these technicians tune engines and keep a high level of performance is through tests on an engine dynamometer.
What Does an Engine Dynamometer Test?
The purpose of an engine dynamometer is to measure engine output to make sure that the configuration is delivering the force that it’s supposed to. To give technicians a sense of how optimal the engine they’re testing is running, they hook up the dynamometer to the engine and let it run. The engine dynamometer will test the horsepower, rotations per minute (RPMs), force, and torque levels to get a sense of the engine’s power.
Calculating Performance
A dynamometer, also known as a “dyno”, is a device that measures force, torque or power. For chassis or engine applications, a dynamometer is designed to create a load to duplicate various speed (RPM) and torque (Nm or lb-ft) requirements. From this data, power (HP or kW) can be calculated. This in turn provides a snapshot of the chassis or engine performance for comparison to the manufacturer’s specifications. Typically, a dynamometer gives the operator the ability to vary the load applied to the unit under test to mimic specific requirements.
Troubleshoot, Identify, Verify
An engine dynamometer is a device used to test an engine that has been removed from a vehicle, ship, generator, or any other piece of equipment powered by an internal combustion engine. The purpose is to confirm performance before the engine is installed back in the equipment. Engine dynamometers can help facilities troubleshoot by determining when an engine is overheating, or by identifying intermittent performance and sensor issues. They also verify the quality of builds, rebuilds, or repairs in a controlled environment before vehicles are put into use.
Engine dynamometers are coupled to the engine under test via a drive or Cardan shaft. Engines are mounted to rolling carts and can be loaded on the cart prior to movement into the dyno room. Typically, engine dynamometers create loads using a water brake, EC or alternating current (AC) design.
Water brakes are designed to test engines rated up to 7,500 kW or 10,000 HP
EC units are designed for lower power engines (less than 400 HP)
AC designs can accommodate a wide range of applications (10 HP to 5,000 HP) and offer exceptional natural (transient) response
Applications for Dynamometers
In addition to being used to determine the torque or power characteristics of a machine under test (MUT), dynamometers are employed in a number of other roles. In standard emissions testing cycles such as those defined by the US Environmental Protection Agency (US EPA), dynamometers are used to provide simulated road loading of either the engine (using an engine dynamometer) or full powertrain (using a chassis dynamometer). In fact, beyond simple power and torque measurements, dynamometers can be used as part of a testbed for a variety of engine development activities such as the calibration of engine management controllers, detailed investigations into combustion behavior and tribology.
In an engine dynamometer, water flow, proportional to the desired applied load, creates resistance to the engine. A controlled water flow through the inlet manifold is directed at the center of the rotor in each absorption section. This water is then expelled to the outer dynamometer body by centrifugal force. As it is directed outward, the water is accelerated into pockets on the stationary stator plates where it is decelerated. The continual acceleration and deceleration causes the dynamometer to absorb the power produced by the engine. Through this transfer of energy the water is heated and discharged.
Measuring how much power you need
If you’ve got something like a giant factory machine made up of levers, gears, drive belts, and other bits and pieces, and you want to know how big an engine or electric motor you’d need to make it work, you can use a machine called a driving dynamometer. It’s essentially just an ordinary engine or an electric motor with some appropriate measuring meters or monitors attached so you know how much power, force, or speed is being used at any given moment.
Measuring how much power you have
If you’ve got an engine or motor, you can use a different kind of dynamometer to measure how much torque (turning force), power, or speed it can produce. Here, the dynamometer acts as a variable load that the engine/motor drives. It works by soaking up or absorbing the power that the engine/motor produces, so it’s called an absorption dynamometer.
An absorption dynamometer is a bit more sophisticated and interesting than a driving dynamometer. If you think about it, it needs a way of soaking up and dissipating potentially a huge amount of power, and there are all kinds of different ways to do this. One easy way is to use electromagnetism.
If you wanted to test out the power of an electric motor, you could connect its driving axle up to the axle of a generator. As the motor spins around, it would make the generator spin too, producing an electric current proportional to the motor’s power; measure the generator current and you have an indication of how powerful the motor is.
Why Dyno Test an Engine?
There are lots of great reasons to perform dynamometer testing on your engine. Learn more here.
If you’re reading this article, you probably already know what it means to dyno test an engine. In short, you power up the engine and add a controlled amount of resistance. From the test, a dynamometer measures your engine’s force, torque, and horsepower. Depending on your career or hobby, these are significant numbers.
But is finding out how many horses you have under the hood the only reason to dyno test an engine? Absolutely not. There are solid, practical reasons to dyno test an engine, bragging rights aside.
Here are a few of them:
To Help Keep Your Engine Running Properly
The computerized dynamometer provides accurate torque and RPM numbers. And then it can accurately measure horsepower. Whoever is tuning your engine now has a basis for changing the engine’s tuning, or they might even recommend changing the engine itself.
These are some of the variables that can be tuned using this method:
- Intake manifold selection
- Ignition timing and advance curve
- Primary tube diameter and length for the headers
- Carburetor spacers
- Cam grind and timing
- Carburetor size and jetting
For an Engine’s First Run
It makes sense to do the first run of an engine on a dyno. Engine break-in routines specified by cam and ring manufacturers can be accomplished under controlled conditions. Blow by can even be monitored as the piston rings seat. The engine can be pre-lubed and pre-heated before every start.
To Find Out the Temperature of Your Exhaust Gas
When it comes to tuning your carburetor—jetting, size, spacers, and fuel distribution—knowing your exhaust gas temperatures is as important (or maybe even more) than horsepower and torque numbers. You could save yourself a major engine repair with this information.
To Get a Written Record of Your Engine’s Performance
A dyno test will give you details about each test, weather conditions on the day of testing, and graphs of your engine’s performance. You can compare your personal performance experiences with the dyno numbers so you can make future adjustments or modifications.
Additional information from the test can indicate both torque and peak torque, plus horsepower, volume metric efficiency, the temperatures of the cylinders and pistons, airflow — I.e., measurements of virtually every engine function.
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