Your guide to using diesel engine specification sheets

So you’re developing a generator set and have selected a couple of engine manufacturers to power it.  You’ve got a design in mind and have your alternator selected.  Now the engine distributor’s sales or application people send you the diesel engine specification sheet.  It’s two or three pages of solid numbers, and the problem is you don’t know which ones are important, which ones affect emissions, and which ones are just for info.

You could contact the distributor, hope that they understand your application and needs, and assume that the answers they give you are correct.  Or you could just spend the time once to learn about these topics and be able to interpret diesel engine specification sheets yourself from now on.  This is what I will help teach you on this website.

In this post I will cover some of the more common and simple terms that you will encounter when evaluating engines.

Engine operating speed & idle speed

Most small, generator-drive diesel engines operate at 1800 rpm or 1500 rpm.  Accordingly, this will give you electricity at 60Hz or 50Hz.

Some electrical appliances are very sensitive to frequency and power quality fluctuations, so more generator-drive engines these days have very precise engine speed governing to maintain frequency.

For heavy duty continuous applications, a slower engine speed will result in a longer engine life, more running hours between maintenance intervals, and a much lower fuel consumption.

With the correct alternator, 1200rpm will give you 60Hz electricity.  Also, 1000rpm will result in 50Hz power.  900rpm is another speed available for 60Hz.

This is very typical of continuous power applications over 1MWe in electrical power output.

Emissions Rating

With strict requirements imposed by the European Union and American EPA, you cannot choose a diesel engine without understanding it’s emissions certification.

It is very important to understand the local emissions requirements when purchasing a gen-set.  It is even more important to know the requirements of your customers when developing a power gen package for sale to industry.

Emissions fines are legit and, for the small packager, could be bankrupting.

To determine your requirements, you have to understand the differences between portable, stationary, and emergency applications.

Also, the engine’s power rating, and not the electrical power  output rating, determines the emission’s envelope that the product falls into.

Other parameters are also affected by the emissions rating, including:

• Fuel consumption
• Load pickup and block load capability
• Exhaust back pressure requirements
• Fuel quality requirements
• Ability to self diagnose, calibrate, maintain, and repair

The type of technology used to achieve an emissions rating certification can affect these important areas.

Droop or isochronous running

With most standalone generator sets, it is desired to not have engine speed change with increasing electrical load.  This is a zero droop situation.

Though it is more common with non-generator drive industrial engines, sometimes the engine speed must change, especially when attempting to parallel with another generator set – or with the electrical grid.

Normally, I aim to only cover generator drive engines on this blog, but many of us are also involved with industrial and construction equipment that uses variable speed engines as well (think hydraulic power units, air compressors, rock crushers, cranes, etc.).  I will sometimes provide comments on my experiences outside of power generation, and the topic of governor droop is an important one to expand upon.

In a non-electrical application, droop is a commonly found.  It allows the engine speed to slightly drop as load increases.  In theory, this isn’t good since most small-displacement, high-speed diesel engines make the most power at the rated high-idle speed.  With the advanced turbocharging systems that these engines possess, an could be fully loaded

Altitude capability

Whenever possible, it is best to know the altitude of the location you will be generating power for.

This info also helps you determine how large of a displacement and what type of technology an engine requires.

As altitude increases, the amount of oxygen in the air decreases.  This not only affects our breathing, but an engines breathing as well.  You have definitely noticed this if you have been hiking in high mountain regions.

Many older, naturally aspirated diesel engines have problems pulling their full rated loads at altitude.  They smoke, sputter, and just quit.

The higher the altitude, the more extreme this effect becomes, and the less power an engine can make.  This is called a derate.

This problem can be countered with proper understanding of engine displacement and turbocharger technology.

In this post I discussed a few important parameters that you will encounter on diesel engine specification sheets.  There are dozens more, and I will cover them over time in this blog.

I am always open to topic suggestions, so please let me know what engine applicaiotn problems you are having.

If you have specific diesel engine specification sheets and questions that you would like interpreted on here, please send to me in an email.

For private advise, please visit my consulting services page.  All consultation projects remain confidential and do not end up on this blog.