Different types of vehicles operating in various industries also have different prerequisites in how they can be operated. Therefore, it is important to have an engine that is adjusted to fit your specific vehicle and still maintains high uptime, is reliable and lives up to emission legislations. This is the third part in our article series about engine technology where I will describe a heat management system and cover the basics of Exhaust Gas Recirculation, Electrical Exhaust Pressure Governor and air inlet throttle. Also, I will share some tips that can help you decrease your fuel consumption even more!
An integrated part of the engine’s control system
A prerequisite for the exhaust aftertreatment system to function is that the system is provided with the right amount of heat. Therefore, when the exhausts leave the engine and enter the exhaust aftertreatment system they must be over a certain temperature limit. The exhaust heat is controlled by the engine’s heat management system. The heat management system consists of an Exhaust Gas Recirculation (EGR), an Electrical Exhaust Pressure Governor (EEPG), an air inlet throttle as well as a common rail injection system. However, the heat management system is not a separate system but an integrated part of the engine’s control system. Thus, the heat management system and all its components are controlled by the Engine Management System (EMS).
Avoid stand still regeneration on engines with low load and speed
As described in part two of my article series, “Exhaust aftertreatment system – a cleaning process for exhausts“, if a vehicle is driven with high load and speed the engine will produce enough amount of heat so the exhaust aftertreatment system functions on its own and can perform passive regeneration on the DPF. However, if a vehicle is driven with low load and speed the engine will not produce enough heat. In this case, the heat management system will be useful as it helps increase the heat in the engine and avoid a stand still regeneration.
How an engine operates can be explained by three different engine modes: normal operation mode, moderate heat mode and high heat mode. Normal operation mode is when the engine has a good fuel consumption and is driven so it generates sufficiently high temperature on its own to perform passive regeneration. Moderate heat mode is a moderate increase of the engine temperature, which also has an affect on the fuel consumption. This is the first step to increase the engine’s temperature. High heat mode is the second step in order to increase the engine’s temperature, which is done by activating the eEPG. If high heat mode can’t produce high enough temperatures, the vehicle must perform stand still regeneration.
EGR – reinserts exhausts into the engine to raise the temperature
The concept of EGR means to reinsert a certain amount of exhausts into the engine to raise the temperature. When the exhausts are reinserted in the engine, they go through the combustion process one more time. Since the exhausts that are reinserted already are heated, this helps increase the temperature in the engine. The EGR is attached on the exhaust side of the engine to collect heated exhausts, which are then transported through a pipe to the inlet side of the engine. To enable the transportation of exhausts, there must be a higher pressure on the exhaust side than the inlet side of the engine. There are two different EGR systems to choose from: uncooled EGR and cooled EGR.
Uncooled EGR vs Cooled EGR
When the exhausts come out from the combustion process they are so hot that they need to be cooled down before they can be reinserted in the engine. Uncooled EGR means that the exhausts are cooled down by the fresh air entering the engine. However, fresh air can only cool down the exhausts to a certain extent. That means uncooled EGR only allows for a limited amount of exhausts to be reinserted in the engine. As a result of using uncooled EGR, the engine will produce more NOx, which in turn will require a larger exhaust aftertreatment system.
The exhausts from a cooled EGR, on the other hand, are not only being cooled by fresh air but also by passing through a cooler that is mounted on the pipe going from the exhaust side to the inlet side of the engine. Therefore, cooled EGR enables a larger amount of exhausts being reinserted in the engine compared to uncooled EGR. Cooled EGR can be utilized over the engine’s entire speed/load range and results in lower engine out NOx, which in turn leads to a smaller exhaust aftertreatment system. However, the engine requires more from the cooling system, which could mean that a larger radiator is needed. Another challenge with using cooled EGR is that the cooler can become clogged when water condense mixes with soot.
eEPG and air inlet throttle regulate the pressure in the engine
If the cooled or uncooled EGR is running but the process of incinerating the soot in the DPF is too slow, the engine automatically goes into high heat mode and switches off the EGR and starts the eEPG instead. This is an effective method to quickly increase the engine’s temperature in order to avoid a stand still regeneration. The eEPG is an electric throttle that regulates the exhaust gas pressure. It is placed in the exhaust pipe after the turbo and enables the exhaust pipe to close almost completely. When the exhausts are captured in the engine it will create a high pressure, which in turn will lead to increased temperature. However, using the eEPG also means that the fuel consumption goes up. Therefore, the eEPG should only be used when necessary. The amount of time the eEPG needs to run depends on the load and speed of the engine. Thus, if the engine is driven in normal or moderate mode, the eEPG does not have to be used at all.
The air inlet throttle has the same function as the eEPG but is instead located on the inlet side of the engine. The difference between the air inlet throttle and the eEPG is that the air inlet throttle is used to create pressure in order for the EGR to function. Thus, the air inlet throttle and the EGR work together, compared to the eEPG that works alone. Therefore, the air inlet throttle and the eEPG are never used at the same time. The air inlet throttle is also used to regulate so the right amount of exhausts from the EGR enters the engine.
Insulated pipes and start/stop function help decrease fuel consumption
There are also other aspects to consider in order to maintain a high temperature in the engine. For example, it is crucial that the pipes going from the engine to the exhaust aftertreatment system are insulated. A good insulation decreases the risks of letting out valuable heat, and the engine can operate less in high heat mode, which leads to high fuel consumption. Another valuable aspect to consider is the start/stop function. When the engine runs idle, the whole engine system is cooled down. Therefore, it is better to turn off the engine and stop the exhaust flow. An insulated engine will keep the heat inside so when the engine starts again, the NOx reduction in the exhaust aftertreatment system can start right away. In addition, by turning off the engine the overall fuel consumption decreases, since no fuel will be used at all if the engine is not running.
Volvo Penta’s Stage V engine suits multiple applications and needs
Volvo Penta offers an automatic start/stop function to our Stage V solution. To be able to offer our customers a reliable and effective engine that maintains high uptime, we have chosen uncooled EGR in our Stage V engines. When designing our Stage V engines, we have focused on a solution that fits many different applications and needs. We want our customers to continue with their successful businesses and not have to worry about exhaust gases and having to stop their vehicles when they are needed the most. Thus, we believe our Stage V engines are the best solution for both the environment as well as our customers, irrespective of industry.
As you probably already have figured out, the EGR needs another component to be able to function in the best way possible. Therefore, our fourth and final blog article in our article series will describe the turbo and what different turbo solutions there are to choose from. Don’t miss out!
I hope you enjoyed reading the third blog article in our article series about engine technology. Feel free to ask me any questions, visit our website or our Professional Power blog for more interesting articles!