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EMISSION CONTROL - V8 DESCRIPTION AND OPERATION 17-2-11 Exhaust Emission Control System The fuel injection system provides accurately metered quantities of fuel to the combustion chambers to ensure the The main components of the exhaust emission system are two catalytic converters which are an integral part of the x ) and hydrocarbons (HC). The active constituents of the catalytic converters are platinum (Pt), palladium (PD) and rhodium (Rh). Catalytic converters for NAS low The two catalytic converters are shaped differently to allow sufficient clearance between the body and transmission, The basic control loop comprises the engine (controlled system), the heated oxygen sensors (measuring elements), The reliability of the ignition system is critical for efficient catalytic converter operation, since misfiring will lead to CAUTION: If the engine is misfiring, it should be shut down immediately and the cause rectified. Failure to do CAUTION: Ensure the exhaust system is free from leaks. Exhaust gas leaks upstream of the catalytic CAUTION: Serious damage to the engine may occur if a lower octane number fuel than recommended is used. Air : Fuel Ratio The excess air factor is denoted by the Lambda symbol λ , and is used to indicate how far the air:fuel mixture ratio deviates from the theoretical optimum during any particular operating condition. l When λ = 1, the air to fuel ratio corresponds to the theoretical optimum of 14.7:1 and is the desired condition for minimising emissions. l When λ > 1, (i.e. λ = 1.05 to λ = 1.3) there is excess air available (lean mixture) and lower fuel consumption can be attained at the cost of reduced performance. For mixtures above λ = 1.3, the mixture ceases to be ignitable. l When λ < 1, (i.e. λ = 0.85 to λ = 0.95) there is an air deficiency (rich mixture) and maximum output is available, but fuel economy is impaired. The engine management system used with V8 engines operates in a narrower control range about the stoichiometric λ = 0.97 to 1.03 using closed-loop control techniques. When the engine is warmed up and operating under normal conditions, it is essential to maintain λ close to the ideal ( λ = 1) to ensure the effective treatment of exhaust gases by the three-way catalytic converters installed in the downpipes from each exhaust manifold. Changes in the oxygen content has subsequent effects on the levels of exhaust emissions experienced. The levels |