Research studies have shown that industrial activity is directly related to the demand for electric motors and back-up power through diesel generators for operational support. The most prevalent end-use applications for generators include: industrial plants, manufacturing, construction, chemical applications, petrochemicals, agriculture, automotive, mining, oil and natural gas, telecommunications and healthcare.
Responses to climate change and energy efficiency worldwide have led to global fuel-source trends that would initially appear to reduce considerations given to diesel power, and increase the share of renewable and natural gas power applications in the power-supply mix.
Nalen Alwar, Projects Sales Manager for Cummins Power Generation Southern Africa, points out that diesel fuel is still by far the most widely-used fuel source, especially in developing nations and emerging markets. “A well-established supply chain exists in Southern Africa, where diesel-generated power has shown advantages of project simplicity, short project lifecycles, lower capital cost and rapid installation time for power on-stream.”
According to Alwar, there have been key challenges with regard to operating cost and emissions levels, and it is worthwhile exploring how technological development has addressed these. “Falling crude oil prices have lowered diesel prices and impacted alternative-energy investment drivers. Furthermore, the concept of resilience through hybrid solutions has meant that diesel-generated power has to feature as a relevant component.”
Alwar also reveals that instability in stakeholder structures for projects with alternate fuel feedstock, together with decreasing levels in dams and lakes, which has affected the performance output of hydropower plants, has yet again resulted in diesel-generated power being called on as emergency measures in Southern Africa.
A topical issue is whether diesel power would still be relevant in the future. Climate trends are now demanding that all users of power employ tactics to reduce harmful emissions that impact the environment, and renewable energy solutions are advancing beyond the infancy stage of the technology lifecycle in Southern Africa.
“However, diesel power is still the mainstay solution for operational resilience and industrialisation in remote areas. Significant technology improvements have been made towards reduction in capital, operating costs and environmental stewardship,” states Alwar.
Compact designs have resulted in footprint reductions and increases in power output have been achieved by increasing cylinder peak pressure, while also reducing the conventional number of cylinders required. Ductile iron blocks with the highest structural strength are used to achieve multiple overhauls, with minimal remanufacturing. Durable pistons can be forged from a single piece of steel, allowing reuse at the rebuild stage.
Alwar elaborates: “Premium materials are used for piston rings and hardened cylinder features, together with enhanced piston cooling, reduced piston-ring temperatures and increased wear resistance and cylinder life. This reduces total lifecycle costs.”
Efficiency of diesel
The efficiency of a diesel engine is most directly tied to combustion rate – the degree to which the fuel is completely burned during ignition. This is typically a function of how finely and evenly dispersed the fuel is during injection into the combustion chamber. Turbocharging, which forces excess air into the chamber, also improves the combustion rate, which is why two-stage turbocharging, with intercooling between the stages, is now common for diesel gensets.
Alwar explains that a Modular Common Rail System (MCRS) enables diesel engines to achieve exceptionally low fuel consumption for their power output. “The MCRS injectors are capable of extremely high-pressure injection, which leads to a reduction in particulate matter emissions. This method replaces traditional mechanical injection with electronically-controlled multiple high-pressure injections during each combustion cycle,” he continues.
Rather than rely on separate injectors controlled by a camshaft, it uses a single system that supplies all the injectors in the engine with a common source of fuel. This allows much higher fuel pressures than a mechanical injection system, which maximises vaporisation of the fuel, and thus combustion rate. Modern high-pressure common-rail diesel fuel systems allow for much higher fuel pressures, and much more precise and flexible injection of fuel into the combustion chamber.
Meeting international environmental standards
To meet Tier 4 low-emission standards as set out by the US government’s Environmental Protection Agency (EPA), Selective Catalytic Reduction (SCR) technology has been used successfully on new Cummins diesel gensets to reduce NOx emissions by as much as 95%. Another method often used with SCR is exhaust-gas recirculation, which sends part of the exhaust gases back to the combustion chamber. This lowers the adiabatic flame temperature, allowing for lower temperature combustion and reduced NOx production.
SCR also results in 5% more fuel efficiency. “Digital controls are essential for the newest gensets, which rely on high-pressure common-rail fuel-injection systems and precise control of ignition and combustion. They are also necessary where tight emissions compliance is a consideration,” explains Alwar.
Another advantage is that digital controls can monitor the real-time state of a wide variety of operating parameters, and display them on a centralised panel, as opposed to less sophisticated analogue systems. Alwar indicates that this allows operators to identify and correct faults much more quickly, leading to more reliable power and less downtime. “What is more, they also allow for remote monitoring and operation.”
The future outlook
With diesel gensets typically representing either emergency generation or generation where there may be no grid power to fall back on, these are critical considerations. Oil-management systems that replenish oil automatically, based on engine-load factors, fuel filtrations systems with enhanced durability, high-pressure fuel systems and prognostic capabilities, are other improvements that reduce operating costs.
Alwar points out that the rise of distributed generation through decentralised power supply schemes are evolving further. “Decentralisation is not just about displacement of grid power with one energy source, but how to optimise decentralised systems with various fuel sources to achieve energy efficiency, reliability and critical process protection.”
A typical scheme could comprise renewable power generation sources such as wind and solar. However, Alwar believes that these pose challenges to system reliability and performance, given their inherent intermittent contribution and associated disturbances. “Gas-to-power programmes in Southern Africa are yet to overcome challenges such as natural-gas pipeline infrastructure and moderating market prices.”
He indicates that diesel-engine power plants have synchronous technology and contribute a high level of operational stability for standby or prime power applications, together with mature diesel-fuel supply chains. “Manufacturers of diesel gensets are making steady technological gains that reduce capital intensity and emission levels, and enhance power output and efficiency. Diesel-generated power is still likely to feature on its own or incorporated into hybrid solutions for many more years,” Alwar concludes.
References and recommended reading:
Overton, TW., “Diesel Gensets Aim at the Future”, Power Magazine , 2015
Natekar, A & Menzel, M., “The Impact of Tier 4 Emission Regulations on the Power Generation Industry”, Power Topic #9010 Technical Information from Cummins Power Generation, 2010
Cummins Inc., a global power leader, is a corporation of complementary business units that design, manufacture, distribute and service diesel and natural gas engines and related technologies, including fuel systems, controls, air handling, filtration, emission solutions and electrical power generation systems.
Headquartered in Columbus, Indiana, (USA) Cummins currently employs approximately 54,600 people worldwide and serves customers in approximately 190 countries and territories through a network of approximately 600 company-owned and independent distributor locations and approximately 7,200 dealer locations. Cummins earned $1.65 billion on sales of $19.2 billion in 2014.
Cummins South Africa is headquartered in Johannesburg, with branches in Longmeadow, Bloemfontein, Cape Town, Durban and Port Elizabeth.
Susan S Quist