Page 49 - Energize July 2021

TECHNICAL

Diesel generator standby and

mobile plant developments

by Mike Rycroft, Now Media

The field of standby and mobile power systems has expanded and now includes such items as micro
gas turbines, gas internal combustion engines and fuel cells. The diesel generator set is, however, still the
mainstay of standby and mobile plant, and developments which make diesel generator sets more efficient, n
flexible and less polluting will ensure their use for years to come.

ith the increase in load shedding and grid failure, having a Diesel generator developments
reliable source of standby plant which can run for several Although the basic configuration of the diesel generator set remains
Whours at a time is essential for continued operation in very much the same, there have been a number of significant
both commercial and industrial applications. Diesel is still by far changes in the mechanical construction, the components making
the most widely used fuel source especially in developing nations up the machine, and most importantly, the use of (electronic) digital
and emerging markets. Fortunately, a well-established supply devices for the monitoring and control of the diesel generator set.
chain exists in Southern Africa. Diesel-generated power has shown
advantages of project simplicity, short project lifecycles, lower Mechanical
capital cost and rapid installation time for power on-stream. 1 Compact designs have resulted in carbon footprint reductions, and
In addition to the classical application of standby or mobile increases in power output have been achieved by increasing cylinder
power units, diesel generator sets are finding increasing application peak pressure, whilst also reducing the conventional number of
in large hybrid power systems, particularly for remote mines. Pairing cylinders required. Ductile iron blocks with high structural strength
diesel generator sets with solar is proving to be a highly compatible are used to achieve multiple overhauls with minimal remanufacturing.
and competitive option for off-grid applications. Solar-diesel Durable pistons can be forged from a single piece of steel,
hybrid plants offset the two main drawbacks of each option: The allowing reuse at the rebuild stage. Premium materials are used
intermittency of solar photovoltaic (PV) generation and the high for piston rings, and hardened cylinders, together with enhanced
cost of transporting diesel fuel to a remote operation. Several such piston cooling, reduce piston ring temperatures and increase wear
hybrid systems have been completed or are in the planning stage in resistance and cylinder life. This reduces total lifecycle costs.
Southern Africa.
Electricity from solar PV in most cases costs less than from Efficiency
diesel generation, but, without battery backup, there is no power Efficiency in a diesel engine is most directly tied to combustion rate,
at night. That’s where the diesel genset, which can be cheaper per the degree to which the fuel is completely burned during ignition.
kWh than a long duration battery, comes in, and combining the two This is typically a function of how finely and evenly dispersed the
2
can result in substantial savings on power costs. A study estimated fuel is during injection into the combustion chamber. Keeping diesel
that mining projects employing solar-diesel generation could fuel competitive has resulted in an array of changes to improve
substantially reduce overall costs of power to the mine operators. efficiency and reduce emissions.
Fixed solar-diesel hybrid plants have been in operation at remote Perhaps one of the most significant developments has been
sites for several years. the adoption of the modular high pressure common rail (HPCR) fuel
injection system (see Figure 1). The classical method of fuel injection
Diesel generator setbasics uses mechanically controlled injectors operating from a low-pressure
Compared to other options such as gas engines, microturbines, feed line. The HPCR system uses electronically controlled multiple
fuel cells and renewable sources such as wind and solar, diesel high-pressure injections via a single system which supplies all the
generators are typically the least expensive in terms of capital injectors in the engine with a common source of fuel. This allows
outlay. Diesel fuel also has substantially higher energy density far higher fuel pressures than a mechanical injection system, which
than natural gas and other options, which can simplify fuel supply maximises vaporisation of the fuel and combustion rate, which in
logistics. Diesel generators have a very long service life and can be turn allows for far higher fuel pressures and a significantly more
overhauled several times before reaching end of life. precise and flexible injection of fuel into the combustion chamber.

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