Design Modifications

Towards cleaner diesel generators and engines

Diesel generators (DGs) are being used across industries as an alternative to grid power to support their operations. In recent years, several technological innovations have been undertaken in DG sets in order to reduce noise, control emissions, and increase power output and efficiency. Several advanced technologies have been introduced to make the gensets more compact and suitable to be used in extreme climatic conditions. These include common rail direct fuel injection (CRDi), exhaust gas recirculation and selective catalytic reduction. Further, the shapes of combustion chambers are being modified to maximise the fuel efficiency. One of the key emerging trends in the DG space has been the use of electronic control systems, which allow remote monitoring of the system.

A look at the key technology trends in the diesel genset and engine space…

Fuel efficient technologies

To increase fuel efficiency, manufacturers are developing large-sized DG sets with ratings of up to 5 MW for critical standby power and/or for continuous operations. Some of the advanced technologies being used are as follows:

Common rail direct injection

In a CRDi system, fuel is injected from the fuel tank directly into the combustion chamber. The “fuel-rail” stores fuel and supplies it to the injectors at the required pressure. It acts as a shared fuel tank for all reservoirs. CRDi is an electronically monitored injection system that controls the timing of the fuel injection as well as the amount of the fuel injected. CRDi allows for finer vaporisation by homogenising the mixture of fuel and air. This not only increases power output and improves fuel efficiency, but also helps in reducing exhaust emissions.

Hybrid technologies

Hybrids and multifuel technologies have been in use for some time by captive power plants. These help increase system reliability, enhance efficiency and achieve cost savings. Telecom tower operators are also opting for hybrid solutions. Hybrid power systems combine at least two different sources of energy. These systems may or may not have a storage facility. The most common hybrid technologies used are solar photovoltaic (PV) and diesel engines. Meanwhile, multifuel technology based plants allow the use of biomass feedstock and coal interchangeably.

A solar PV-diesel hybrid system seeks to maximise the load on the PV system and minimise it on the DG set. If adequate power is available from the PV array, some of the gensets may be completely shut down. In a plant with a battery set-up, besides meeting the excess load, the genset recharges the battery if needed. This system can be scaled up from a few kilowatts to a megawatt at least. System sizes can be expanded easily if required. The actual configuration of these systems varies as per the load requirements, location, solar radiation levels, etc. The key advantages of hybrid power systems are cost efficiency as they reduce dependence on expensive diesel fuel; clean energy generation, which helps meet environmental norms; and uninterrupted power supply that resolves intermittency issues.

WHR systems

Another way of improving engine efficiency is the deployment of waste heat recovery (WHR) systems along with DG systems, particularly in industries that use DG sets to meet most of their captive requirements. A WHR system recovers heat from steam and transforms it into electrical energy for utilisation. This is done using energy conversion devices like regenerators, recuperators and economisers. By using a WHR system, energy consumption can be reduced by 5-30 per cent.

Emission control technologies

The Central Pollution Control Board has been regulating emissions from diesel generators at the manufacturing stage through product certification since 2005. In March 2016, the Ministry of Environment, Forest and Climate Change (MoEFCC) notified environment standards for gensets running on liquefied petroleum gas (LPG)/liquefied natural gas (LNG), diesel with LPG/LNG and petrol with LPG/LNG. The standards were notified with an objective to control emissions and noise across different categories of gensets. These standards are expected to be revised every four to five years. Some of the technologies available for reducing emissions include:

SCR

It is one of the most cost-effective and fuel-efficient emission control technologies available for DG sets. In selective catalytic reduction (SCR) technology, a liquid-reducing agent is injected through a special catalyst into the exhaust stream of a diesel engine. The reducing agent is usually automotive-grade urea, which is known as diesel exhaust fluid (DEF). The DEF sets off a chemical reaction that converts nitrogen oxides into nitrogen, water and tiny amounts of carbon dioxide, which are natural components of the air. These are then expelled through the vehicle tailpipe. SCR technology enables NOx reduction reactions in an oxidising atmosphere. The technology is called “selective” because it reduces the levels of NOx using ammonia as a liquid reducing agent within a catalyst system.

EGR

Diesel combustion occurs at very high temperatures and releases NOx as a by-product. NOx emissions need to be regulated as per the environment norms. Exhaust gas recirculation (EGR) is one of the technologies being used by diesel engine manufacturers to lower the NOx emissions in the diesel combustion process. In EGR systems, a part of the exhaust gases is re-circulated into the engine, which contains the unburnt fuel and carbon. This process decreases the temperature and increases the heat capacity of the mix allowing for combustion at a much lower temperature, thereby reducing NOx formation.

Smart DG sets

Smart DG sets consist of digital controls as against analog controls installed in conventional systems. Digital controls are highly integrated and report the real-time status of all aspects of a diesel engine – fuel, engine oil, coolant, engine temperature, battery status, transfer switch status, etc. These systems can be connected to a computer to enable remote monitoring of operations. They report the nature and place of a fault in real time, which can be corrected remotely. This also saves a lot of space as a digital control system integrates all the functions of a diesel generator, as against analog control systems that have separate control modules for each function. Smart DG sets help in achieving stable voltage and output frequency, thereby increasing system reliability. Digital controls also increase fuel efficiency and reduce emissions by making automatic adjustments to the fuel rate input and injection timing under varying load conditions.

Conclusion

Although the DG industry has been facing a number of challenges of late owing to stringent environment regulations and norms, it continues to be the most preferred means of back-up power. Various technological developments and advancements have taken place in response to the government’s increased focus on emission control. This has helped the industry hold its position in the market. However, the development of a fully clean diesel technology is crucial going ahead, especially in view of the growing use of renewables and the need to curb emissions.

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