Toyota showed a recirculation system at the Vienna Motor Symposium that reduces both nitrous oxides (NOx) and particulate matter in diesels.
Several manufacturers are developing systems to recirculate exhaust gas within the engine as a way to reduce emissions of NOx. Mixing exhaust gases with the fresh air-fuel mixture is a proven way of lowering NOx emissions.
Most diesels require separate filters. Toyota's diesel NOx particulate reduction system is contained in a catalyst directly behind the engine, rather than the normal position in the middle of the exhaust pipe.
Toyota improves performance by cooling the gas used in the exhaust recirculation system. The engine's common-rail fuel injector achieves higher pressures, and the multi-point injection attains the low-temperature combustion needed to reduce the engine's basic emissions level.
Further emission reductions come from injecting tiny amounts of fuel from the common-rail system into the exhaust manifold, enough to create the stoichiometric conditions to burn fuel completely.
The Toyota diesel complied with the European Euro IV emissions standard that becomes effective in 2005.