Ford's Low-Cost Reductant System: Big Breakthrough

Diesel Fuel News, Oct 15, 2001 by Jack Peckham

Ford Motor Co. has developed an on-board reductant injection system for diesel emissions control that not only beats conventional systems on cost but also is much simpler, quieter, 75% lighter, more compact, more efficient, more durable and plugging-resistant.

The new system is compatible with onboard diagnostics (OBD) and provides "accurate, excellent dispersion" of diesel fuel or urea solution for vehicle after treatment devices to reduce nitrogen oxides (NOx) or particulate matter (PM), Ford reports in a paper (SAE 2001-01-3622) that was scheduled for delivery at last month's Society of Automotive Engineers fuels & lubes conference.

The system is designed to inject fuel or urea solution immediately upstream of a diesel oxidation catalyst, non-thermal plasma catalyst (NTPC) system, selective catalytic reduction (SCR) unit, lean-NOx trap or diesel PM filter. This scheme thus avoids problematic in-cylinder post-main injection of fuel that can cause oil dilution, engine wear and "soot wetness" that can lead to EGR valve plugging.

The new Ford system eliminates components such as dryers, accumulators, pressure regulators, thermal and pressure switches, high pressure liquid pump and avoids the high temperature, high pressure, high-electric-current-surge of conventional reductant injector systems that can cause more frequent component malfunction or failure.

Ford instead substitutes a system with just three components: a small air compressor (controlled by engine electronic control unit), a differential pressure sensor and a metering pump/mixer, using less than 10 psi air pressure differential across injection nozzle and 12 watts average power.

Flow rate can be precisely controlled with a small metering pump using frequency and pulse-width modulations. This scheme also eliminates the corrosion problems that can occur with conventional liquid pumps for urea injection schemes. Nor is there any need for high-cost, corrosion-resistant stainless steel.

"The beauty of the Ford system is the capability of tracking the exhaust gas pressure, which fluctuates with engine speed, load and soot filter loading," Ford researcher George Wu-told us in an interview. "This allows the use of a small pump to provide just enough air pressure to provide good injection dispersion. It greatly reduces the weight, volume and power consumption.

"Most other systems fix the air pressure at a high constant value to overcome maximum exhaust pressure, thus requiring a larger pump, higher power and higher operation noise."

Vehicle tests showed the system could achieve over 90% NOx reduction when injecting urea for an SCR catalyst whenever catalyst temperature exceeded 180[degrees]C, with very low ammonia slip (less than 10 mg/mile).

Cost is another key factor, as today's conventional reductant delivery systems are expensive. Some reductant injection systems (for urea-SCR, for example) currently cost many thousands of dollars, but the Ford injection system could dramatically slash costs -- by more than 90%, Wu said. Even when reductant systems are in mass production for original equipment manufacturers (OEMs), the Ford system will cut at least $200 per unit from the best conventional production systems, he said.

Potentially, this represents hundreds of millions of dollars of cost savings when reductant systems are installed on millions of new (and retrofit) diesel engines as is expected world-wide during this decade.

Now that Ford has secured patents on the system, technology licensing will be available from Ford Global Technology Institute, Wu said. (More info: gwul@ford.com).