IMI Precision Engineering, part of the IMI group, designs and manufactures quality fluid control systems for discerning industrial clients. Its innovative technologies, built around valves and actuators, enable vital processes to operate safely, cleanly, efficiently and cost effectively. IMI employs over 12,000 people, has manufacturing facilities in more than 20 countries and operates a global service network.
With a changing global economic climate, capital-intensive truck manufacturers are facing big challenges that are compounded by increasing competition. There is a global trend to facilitate a more sustainable society by reducing pollutant emissions and providing long-term energy efficiency and related cost savings. This trend is reinforced by regulations that impose significant constraints on original equipment manufacturers (OEMs).
The exhaust heat recovery (EHR) with Rankine cycle technology is a very capable solution that has been under development by all major truck manufacturers for some time.
In modern trucks, about one-third of the energy contained in the fuel is lost through the exhaust system. Exhaust gas carries a huge amount of energy that is also referred to as “waste heat.” Exhaust heat recovery increases the overall efficiency of the engine by lowering fuel demand. Heat recovery units are used to recover exhaust heat and transform it into electrical or mechanical power, also enabling engine size reduction.
This complex system requires a full understanding of all the subsystems and components that must be taken into account early in the design cycle, in order to reduce development time and component costs. This type of detailed procedure is exactly what mechatronic system simulation is meant to address.
IMI Precision Engineering (IMI) designs, manufactures and services advanced products that control the precise movement of fluids in difficult conditions. Its innovative technologies are built around valves and actuators, and enable vital processes to operate safely, cleanly, efficiently and cost-effectively. The commercial vehicle group within IMI develops an extensive range of cab, chassis and powertrain solutions that are designed to deliver fuel efficiency and reduce emissions for the world’s leading truck manufacturers in Europe, North America and Asia.
The IMI group is currently focusing on the development of proportional control valves for exhaust heat recovery systems. These valves not only provide a smooth response, low noise and a long, trouble-free lifecycle, but they also play a major role in controlling the efficiency of the system.
In order to recover exhaust heat energy, the Rankine technology uses a working fluid that runs through a boiler system to produce superheated vapor. This vapor is then expanded in an expansion machine, such as a turbine, to produce useful work. This work can be used to produce additional power for every liter of fuel consumed. In this way, IMI is developing unique valve solutions to control the flow of liquid, vapor, exhaust gases and coolants in Rankine cycle heat recovery systems.
However, sometimes exhaust heat is at a low temperature, making it potentially difficult to efficiently utilize the heat. In these cases, the proportional valves bring an additional benefit by regulating the flow rates in the system, enabling heat recovery to occur more often. The result is minimized fuel consumption.
In addition, there are also multiple aspects that must be taken into account while modeling this complex system: a variable heat source due to transient driving cycles; limited cooling that must be balanced in the exhaust gas recirculation (EGR) system; the expansion machine cannot always operate.
The complexity of two-phase fluid analysis led IMI to seek alternatives for simulation, results analysis and design as there was no system in house for the purpose. The model-based systems engineering (MBSE) approach stood out as a compelling strategy to model the highly dynamic nature of the Rankine cycle.
Market pressures as well as client demand for more detailed and optimized information about products required IMI engineers to better understand their systems, specifically the valves.
Simcenter Amesim™ software from product lifecycle management (PLM) specialist Siemens Digital Industries Software is used by IMI for two main purposes.
The first application is for valve characterization. Simcenter Amesim allows engineers to assess valve behavior and performance under dynamic pressure, temperature and phase conditions, and also identify possible failures modes. To do so, engineers must first model each valve and system component, taking into account the main valve characteristics, such as spring stiffness, friction and orifice size. As an example, for sizing and optimizing the functioning of a valve that must survive a vibration test, the IMI team uses Simcenter Amesim to simulate the behavior of the valve. One way do that is by changing the damping. There is a small orifice that a liquid has to flow through as the valve moves. By experimenting with the size of the orifice and different masses on the numerical model, they were able to optimize the complete valve system.
Simcenter Amesim is also used by IMI for valve control feedback validation. Controls for solenoids are simulated using a separate magnetic modeling package. The data is then imported into Simcenter Amesim for simulation of the mechanical properties of the actuator to see how quickly the valve responds to a control request
In addition to detailed valve design, Simcenter Amesim is used as an integration platform to study the overall Rankine system once the IMI valves have been integrated into the vehicle.
“Simcenter Amesim allows us to fully explore an exhaust heat recovery system and understand how IMI valves can improve our customers’ system efficiency and costs,” says Murray Schofield, a simulation design engineer at IMI.
The information on heat recovery systems provided by truck manufacturers and driving cycle data, such as vehicle speed and engine torque requirements, is used to simulate an entire truck with an exhaust heat recovery system according to the World Harmonized Transient Cycle (WHTC) as well as in-house driving cycles.
Furthermore, this type of analysis involves a full thermodynamic simulation. Since there is an ethanol-based liquid flowing through the valves that is meant to be boiled, Simcenter Amesim addresses questions such as: Is it possible to obtain more heat by changing the pressure, or by having a higher mass flow rate? Can engineers get more efficiency out of the system by introducing pressure drops, or bypassing other sections of the system?
“Simcenter Amesim helps us achieve a higher fuel efficiency using our valves,” says Schofield, “increasing fuel efficiency by just 0.1 percent over a 10-year life gives a €1,100 per annum saving for the truck owner.”
Schofield explains the reason for IMI doing such complete simulations: “We must prove that our valves are better than regular valves. For a truck manufacturer, the things that make a component better are more fuel savings, improved system durability and system costs reduction. Simcenter Amesim is allowing us to prove we provide these advantages.”
“When a customer needs a set of data from us, we have been able to utilize the batch capabilities of Simcenter Amesim to quickly simulate and plot many operating points,” says Schofield. “This has been useful because we can now get results in an hour, rather than a couple of days, as used to be the case. The capabilities of Simcenter Amesim that we appreciate the most are the two-phase library, which provides access to all phases of ethanol in an easy-to-use way, as well as the optimization functionalities with 3D plotting and animation to visualize how different parameters affect the system.”
System simulation with Simcenter Amesim is now clearly driving product design within IMI by enabling engineers to significantly cut development time. “The analysis that used to take a few hours using our previous calculation tool now takes five minutes with Simcenter Amesim,” says Schofield.
“Simcenter Amesim has also helped us to increase and optimize the quality of prototypes at every design stage.” It is also important to mention that IMI has built a full Rankine cycle test rig that allows the company to correlate real and simulation data to perform life tests on its valves.
In the future, both fuel prices and the development costs of these systems will determine how fast truck manufacturers will incorporate exhaust heat recovery units. It is expected that exhaust heat recovery units will become more widely accepted within four to six years, promising a bright future for IMI and Simcenter Amesim.