Catalyst Systems

Nett^® catalytic mufflers have been designed to control exhaust emissions and noise from industrial forklift trucks as well as other spark ignited engines used in material handling and construction. The emission control system and the noise attenuation components are incorporated in one shell. All Nett^® catalytic mufflers are designed to match the noise attenuation of the original mufflers they replace.

Three-way catalytic mufflers are the most effective way of controlling carbon monoxide, hydrocarbons, and nitrogen oxides emissions from LPG, CNG, and gasoline engines. CO and NO_x emissions can be simultaneously reduced by 90-99%. Three-way catalyst systems are available in two configurations:

• Closed-Loop Control System. The complete system (see Figure 1—Nett^® system is shown in green) includes a catalytic muffler with built-in three-way catalyst, a zirconium oxygen sensor, and an electronic control unit (ECU). The ECU receives a feedback signal from the O₂ sensor and maintains the engine air/fuel ratio at the stoichiometric point, which yields optimal catalyst performance. This system provides the best conversion of both carbon monoxide and nitrogen oxides and can improve the fuel economy of the truck. Whenever NO_x control is important, use of the closed-loop system is strongly recommended.

• Open-Loop Control System. The catalytic muffler with a built-in three-way catalyst is installed directly into the existing exhaust system. This layout is recommended when CO control is required but NO_x performance can be compromised. The performance of the catalyst will vary depending on the engine A/F ratio (see performance chart in the "Emissions FAQ" section). Operating the truck at a slightly lean mixture will result in good CO abatement. The overall effect greatly depends on the engine maintenance program.