To reduce oxides of nitrogen, a three-way catalyst is required (figure 8.4).

Early Japanese emissions requirements for passenger automobiles required that exhaust gas purification be accomplished by means of a three-way catalyst.

Unwanted reactions can occur in the three-way catalyst, such as the formation of odoriferous hydrogen sulfide and ammonia.

An engine equipped with a three-way catalyst must run at the stoichiometric point, which means more fuel is consumed than in a lean-burn engine.

Volvo was the first automobile manufacturer to employ this technology in the late 1970s, along with the three-way catalyst used in the catalytic converter.

Furthermore, in markets that required emissions controls, the DME also incorporated an upstream O2 sensor and three-way catalyst.

The three-way catalyst developed by them allowed all three exhaust pollutants (hydrocarbon, carbon monoxide and nitrogen oxides) to be remedied using a single catalyst bed.

The three-way catalyst normally used to reduce these emissions does not work for lean air-fuel mixtures, which has kept lean-burn engines from catching on in the United States.

The challenge has been to develop a palladium-only, three-way catalyst that would resist contaminants from engine oils and fuels as well as operate effectively for 100,000 miles, which is a Federal requirement.

In addition, the Cummins engine does not require a three-way catalyst, as the retrofit buses do, to reduce hydrocarbons, nitrous oxides and other pollutants because it generates fewer contaminants from the start.

The three-way catalyst developed by Keith and chemical engineer John J. Mooney with their team at Englehard allowed all three exhaust pollutants to be remediated using a single catalyst bed.

Three-way catalysts are effective when the engine is operated within a narrow band of air-fuel ratios near stoichiometry, such that the exhaust gas oscillates between rich (excess fuel) and lean (excess oxygen) conditions.

Presented in June 1993, the second Evolution version of the Delta HF Integrale featured an updated version of the 2-litre 16-valve turbo engine to produce more power, as well as a three-way catalyst and Lambda probe.

In 1976, the three-way catalyst was introduced, which, after updates, has been able to eliminate 97% of tailpipe hydrocarbon emissions, 96% of carbon monoxide and 90% of nitrogen oxides produced in automobile engines and those used in light trucks and sport utility vehicles.