Bringing the Heat on Cooling Technologies

August 1, 2016

Terry Costlow

Thermal management continues to become more complex as engineers strive to cool engines while generating enough heat to burn away unwanted emissions matter. Ever smarter electronic controls are helping design teams provide optimal performance and long engine life while meeting emissions requirements.

More demanding customers, expanding regulations and growing sophistication at all levels of system design are combining to make thermal management a multifaceted design challenge. Mechanical elements remain a mainstay in the battle to remove heat. But as in many aspects of vehicle design, electronic control units (ECUs) are gaining more of a role.

“Engine electronics can be tailored to the application in order to optimize cooling system operation to engine operation conditions,” said Shelley Knust, Executive Director, Engine Business Unit Off-Highway Engineering at Cummins. “For example, faster engine warm-ups and maintaining optimal coolant operating temperature is desirable to reduce fuel consumption. Electronic controls can enable fine control of the fan speed based on the temperature requirements from engine coolant and charge air requirements.”

Fans are a key weapon in the battle against heat. As variable-speed hydraulic fans displace traditional units, their controls are getting smarter. Pulse width modulation (PWM) is being used to maximize heat removal using minimal energy.

“PWM clutches on fans help keep the engine operating at the right temperature all the time,” said Cedric Rouaud, Chief Engineer for Engines at Ricardo UK. “The speed of the fan and the flow of water can be adjusted or turned on and off with PWM controls.”

When fans run at slower speeds, they’re helping equipment makers meet ever-tightening regulations. Though fans’ fuel consumption and sound levels are small compared to engines, they’re still important. Both fall in correlation with fan speeds.

“Although hydraulic fans and viscous clutches are more expensive than traditional directly-driven fans, they do help to reduce fuel consumption as the fan power can be modulated with the cooling requirement,” said Oliver Lythgoe, Product Concept Marketing Manager at Perkins. “They are also a great tool for reduction of noise, which is regulated in many territories, especially Europe.”

Cooling battery packs

Temperatures inside the engine are just as important as those outside. Microcontrollers also keep engines running at ideal temperatures to get the most from each drop of fuel.

“Electronic controls are also essential in controlling overall heat in the combustion event, and providing the optimal recipe of injection timing and fuel quantity, airflow and quantity, etc. to achieve the desired operating conditions,” Knust said.

While most off-highway design teams focus on engines, others are considering batteries and electric motors, trading one thermal challenge for another. Hybrid technology is sometimes used to augment internal-combustion engines and reduce fuel consumption. That shifts the focus to cooling battery packs.

“With an electric hybrid, you can often downsize the engine,” Rouaud said. “The thermal challenge then becomes keeping batteries at the right temperature. Some OEMs want to use ambient air cooling, but temperatures in the battery pack can go up to 45°C. It’s better to use liquid cooling to keep batteries at 20-30°C.”

Heating after the fact

After fuel is burned, the challenge shifts to preventing emissions from polluting the air. For engineering teams, the question becomes increasing heat rather than reducing it.

“The thermal management of aftertreatment is critical in the latest low emissions diesel engines,” Lythgoe said. “Heat is necessary for the correct operation of the catalytic reaction in diesel oxidation catalysts, selective catalytic reduction systems and in particular to maximize passive regeneration in diesel particulate filters (DPFs).”

The heat used by DPFs comes from engines. Engines designed to run cool must heat DPFs to several hundred degrees centigrade during regenerations. As with most engineering challenges, there are many trade-offs.

“The engine system needs heat at the right place and right time to meet optimal performance and achieve emissions compliance, while reducing the impact to the machine cooling management,” Knust said. “Closed cycle efficiency improvements in the combustion recipe and equalizing flow across the cylinders reduce the amount of heat rejected. Right technology and architecture is a key element of achieving this optimal performance, and our upcoming Stage V engines in the 100- to 515-hp range will utilize a non-exhaust gas recirculation solution, combined with our Single Module Aftertreatment system.”

When aftertreatment system temperatures exceed 500°C (932°F), there’s a danger of burning people or anything else that touches the equipment. Engineers have to devise strategies to increase the internal temperatures of aftertreatment components while protecting operators and the nearby environment.

“Whilst the internal components of aftertreatment best operate warm, it is important to limit the external temperatures, sometimes referred to as aftertreatment skin temperatures,” Lythgoe said. “Perkins choose to insulate aftertreatment components where possible, which has the beneficial effects of maintaining high internal temperature, and also reduces safety risks to operators and service technicians. By keeping aftertreatment skin temperature down, the OEM can reduce the cost and complexity of additional shielding to protect temperature-sensitive components (especially plastics) that are fitted near to the aftertreatment.”

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