700 600 500 400
200 300
100 0
Fuel used (30% load) Fuel used (No load)
44% reduction in fuel
consumed for excercise and maintenance in a single year
Month 12
represents the once-per-year full-load testing of the generator set
0 2 4 6 Months 8 10 12
20 40 60 80 100 120 140 160 180 200
200 180 160 140 120 100 80 60 40 20
00
20 40 60 80 100 120 140
reduction 86% 0
20 40 60 80 100 120 140 160 180 200
0 NOx
reduction PM
42% CO
PLANT MAINTENANCE
30% Load exercising scenario No-load exercising scenario
reduction 82%
reduction
reduction HC
82% pollutants
Above: Figure 4. Consumption data shown here in US gallons, with the generator running at 1800 rpm. Above right: Figure 5. Loaded vs no load monthly exercise pollution creation.
systems which allow better atomisation of fuel into the cylinder.
n More sophisticated engine management systems with ‘fuel mapping’ which, when combined with high pressure common rail systems, can facilitate multiple fuel injections per cycle. This allows near real-time management of the combustion process, enabling it to be better tailored to the requirements of emissions, and/or those all-important cylinder temperatures.
n The addition of charge air cooling allows more low temperature air to be delivered to the cylinder, facilitating more complete combustion of the fuel.
Finer tolerances’ benefits With the much finer tolerances now being achieved in newer pistons and piston ring compared with older engines, blow-by has been significantly reduced, and engine snow burn fuel far more efficiently, mitigating some of the conditions that lead to wet stacking. This is the result of a combination of: n the use of higher cylinder pressures, which increase cylinder temperature at lower loads.
n the addition of common rail systems and fuel mapping. n improved ring designs which better contain combustion gases, and enable a shaped charge to be created (see Figure 3).
When all of these elements come together in one package, the engine can run at much lower load levels when testing on a regular basis. This combination of changes potentially permits generators to be safely run at loads as low as 30% of the rated capacity, or higher as little as once a year, to maintain optimal performance and stay within emissions guidelines. Where budgets permit, many infrastructure operators/ maintenance organisations still undertake generator maintenance in the time-honoured way by conducting load bank testing in accordance with maintenance procedures drawn up many years ago, that have never been revisited. These procedures then, may not embrace many of the technological improvements that have been made, and that can now simplify and reduce the monthly/ quarterly/annual procedure. Many hours of testing and extensive field experience with generators such as the Kohler KD Series (see Figure 3) suggest that a ‘no load’ monthly exercise is allowable, providing that the generator is load bank-tested annually, which is standard practice for many operators, particularly in the data centre and healthcare sectors.
Switch to annual load testing The financial and environmental savings available when switching from monthly to annual loaded testing are quite compelling. By way of an example, a Kohler KD4000/ 3120kW set running at full load for 30 minutes each month will burn approx. 4,400l of diesel fuel per year. If the same testing regime is used, but with monthly no load tests and an annual full load test, approximately 1,160l less fuel per year is consumed, and total pollutant emissions are reduced by 82% (on a pounds per year basis). See Figures 4 and 5. There are also the on-site savings too, such as reduced load bank and associated labour costs.
Actions before revisiting maintenance schedules In the UK, the Medium Combustion Plant Directive (MCPD) became law in December 2017 (Directive (EU) 2015/2193), and covers diesel engines with ratings between 1 and 50 MWth, requiring them to meet a level at or below 190 mg of NOx/Nm3
plus levels of other
emissions too. These ‘medium-sized engines’ represent an important source of emissions such as Nitrous Oxide (NOx) and dust (Particulate Matter). The Directive seeks to regulate the emissions, to reduce the production of these substances known to be harmful to human health. The devolved government of these Isles also carry additional responsibilities for environmental protection, as do local and large city authorities, and it is these local bodies that typically mandate site-specific/local air emissions levels, and permitting of the site or facility. These local decisions, depending on the site, can dictate or influence the testing requirements/regimes adopted especially when using aftertreatment devices. Prior to changing any maintenance procedures, consult with your dealer, service-provider, or the manufacturer. Depending upon the types of exhaust aftertreatments that are fitted to the set, service schedules and capacities may well differ. For example, low-temperature operations in the presence of a SCR emissions control system may run the risk of oxidising stored hydrocarbons and damaging the SCR catalyst, particularly when exhaust temperatures are later raised through load testing or full system operation.
n The author fully acknowledges the major contribution made in the production of this paper by Kohler, and in particular by Brad Meissner, who currently works as a Product manager with responsibility for >700 kW diesel generators at Kohler Co in the US.
Total
70%
Geoff Halliday
Geoff Halliday, Business consultant at WB Power Services, started his career as an apprentice working for Square D (later part of Schneider), before moving into the critical power sector, where he has now worked for over 40 years, splitting his time equally between both the UPS and standby diesel generation sectors. During this period he has held several roles, ranging from Customer service engineer, Project manager, Technical director, and Sales director, through to MD. He said: “The critical power market exposes one to a wide and diverse range of market sectors – including healthcare, life sciences, water treatment, banking and finance, military, manufacturing, and process control, through to data centres of all sizes.” Drawing on his management skills, product knowledge, and ‘vast application experience amassed throughout his career’, Geoff now enjoys sharing his knowledge with others.
October 2025 Health Estate Journal 93
Gallons consumed
Annual emmissions (lbs)
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