As OEs around the world look to downsize engines to help meet the increasingly stringent regulations, EGR systems are becoming more necessary to optimize the powertrain combustion process and improve fuel economy. Because there is limited space in the engine compartment, an emphasis on size reduction is a major factor in developing EGR systems. DENSO’s new and compact EGR cooler will greatly help reduce the overall EGR system size.

—Akio Shikamura, senior executive director of DENSO’s Thermal Systems Business Group

Schematic of an EGR system. Click to enlarge.

Generally, the amount of air drawn into the engine is controlled by the throttle valve. When the engine is not required to produce high power, such as at low speeds, the throttle valve is partially closed. This reduces the amount of air forced into the cylinders, and at the same time the amount of fuel injected is reduced. The air passage section narrowed by the partially closed throttle valve allows a small amount of air to flow into the engine, which increases the engine loss. When the engine loss is high during acceleration or at high speeds, knocking (abnormal combustion) occurs because fuel is burned at high temperature, which reduces fuel efficiency.

To solve these problems, EGR systems recirculate some exhaust gas, instead of using fresh air, into the engine cylinders to reduce piston load while maintaining a small amount of fuel injection. This slows the rise in temperature of the air/fuel mixture, increasing fuel efficiency.

EGR coolers decrease the temperature of hot exhaust gases recirculated into the intake manifold, which also increases the density of the exhaust gas. This helps increase the performance of EGR systems, which reduce engine loss and prevent engine knocking. Vehicles with EGR systems equipped with EGR coolers can potentially increase fuel efficiency by 2 to 3%.

Fin slits. Click to enlarge.

DENSO’s EGR cooler uses finer slits, just 1 mm wide, compared with conventional models with internal fin slits measuring 4 to 5 mm in width, which allows the system to discharge more heat per unit volume. This design enabled DENSO’s EGR cooler to be 30% smaller than the smallest product in the market, while offering equal performance.