NETT TECHNOLOGIES - Three-Way Catalytic Mufflers 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 NOx emissions can be simultaneously reduced by 90-99%. Three-way catalyst systems are available in two configurations: Closed-Loop Control System -The complete system includes a catalytic muffler with built-in 3-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 NOx control is important, use of the closed-loop system is strongly recommended. Figure 1. Closed-Loop Control System Open-Loop Control System - Loop Control System. The catalytic muffler with a built-in 3-way catalyst is installed directly into the existing exhaust system. This layout is recommended when CO control is required but NOx 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.. Figure 2. Open-Loop Control System Oxidation Catalytic Mufflers The oxidation catalyst is an older emission control technology but is still popular in retrofit forklift truck applications. The emission control system in an oxidation catalyst mufflers includes a catalyst and a secondary air intake system. The secondary air is necessary as a source of oxygen for the catalytic oxidation of CO and hydrocarbons. The Nett® air supply system has been unique on the market by combining venturi and check valve principles, to achieve optimal performance under all engine operating conditions (see Figure 3). The check valve works effectively at low engine speeds, letting air in due to exhaust pressure pulsation. The venturi nozzle creates vacuum and draws air most effectively at higher engine speeds. The noise attenuation section consists of a system of baffles and perforated tubes downstream of the catalyst and is not shown in Figure 3. Figure 3. Schematic of Nett® Oxidation Catalyst Muffler Catalyst Durability Nett® catalysts are designed and manufactured to maintain high activity for the entire life-span of the engine. There are, however, circumstances under which the catalyst life might be shortened. There are two major causes of catalyst deactivation: high temperature poisoning. Nett® catalyst may suffer thermal degradation and loss of activity when exposed to temperatures above 650°C (1200°F) for prolonged periods of time. LPG engines have high exhaust temperatures, much higher than diesel and usually higher than gasoline, and may be close to the above limit. Catalytic combustion of carbon monoxide and hydrocarbons further increases the temperature in the catalyst. Good engine maintenance is very important to avoid catalyst overheating. Many engine problems might result in higher than usual exhaust temperatures. Engine misfire is extremely dangerous; unburned fuel is oxidized in the catalyst with a tremendous release of heat. The catalyst shell changes its color to a spectacular cherry-red but the life span of the catalyst could be shortened to a few hundred hours. A pyrometer to monitor exhaust temperature at the outlet from the catalyst may be supplied with Nett® catalytic mufflers. The pyrometer gauge installs in the operator's dashboard to enable action in case of overheating. High exhaust temperatures could be a sign of either a poor engine tune-up with excessive emissions or a more serious engine problem Several chemical elements have the ability to selectively poison or mask the catalyst surface. Some of the substances to be avoided, e.g. phosphorus, may be present in the engine lubricating oil. Catalyst poisoning is usually not a serious problem on LPG engines but may occur as a result of excessive lube oil consumption. Features of Nett® Mufflers Nett® catalytic mufflers present a simple, practical, and cost-effective solution to the problem of carbon monoxide emissions in the workplace. Several advantages of Nett® mufflers make them the superior choice for most LPG engines: High reduction of toxic gases. Carbon monoxide is typically reduced by over 90%. Hydrocarbons are also substantially reduced. The characteristic smell of propane exhaust is virtually eliminated. Excellent noise attenuation. Nett® mufflers match or surpass the noise attenuation performance of the original silencers. Long life and durability. Mufflers are built entirely from corrosion resistant materials: aluminized and stainless steel. Direct-fit design. All models are direct-fit replacements for the original mufflers. Installation time and cost are reduced to a minimum. Standard & Custom Models Nett Technologies have designed direct fit catalytic mufflers for hundreds of models of forklift trucks and other LPG powered equipment. The pre-designed models can be built and shipped within a few days. Some of the more popular models are available from stock. Custom designed catalytic mufflers are available to replace the original muffler for any LPG application. The catalyst for custom models is selected based on the size of the engine. Custom catalytic mufflers are guaranteed to be direct fit replacements for the original silencers. Carbon monoxide emission performance of custom mufflers is also guaranteed, provided the engine is well maintained and no excessive CO emissions are present. Nett Technologies invites inquiries for OEM catalyst systems. OEM applications are developed in cooperation with the equipment manufacturer. The catalyst specifications are optimized to meet the particular emission targets and durability requirements. Also, the design of the muffler, including the catalyst substrate selection, canning technology, and noise attenuation requirements are optimized for the application. Development of OEM exhaust systems includes the design and fabrication of prototypes which are tested for emission and noise performance.