Automotive lean burning

Takahashi, N., Shinjoh, H., Iijima, T. et al. (1996) The new concept 3-way catalyst for automotive lean-burn engine NO, storage and reduction catalyst, Catal. Today, 27, 63. 

Miyoshi, N., Matsumoto, S., Katoh, K. et al. (1995) Development of New Concept Three-Way Catalyst for Automotive Lean-Burn Engines, SAE Technical Paper 950809. 

Takahashi, N., Shinjoh, H., Iijima, T., Suzuki, T., Yamazaki, K., Yokota, K., Suzuki, H., Miyoshi, N., Matsumoto, S., Tanizawa, T., Tanaka, T., Tateishi, S. and Kasahara, K. (1996) The new concept3-way catalyst for automotive lean-burn engine NOx storage and reduction catalyst. Catal. Today, 27, 63-69. 

Matsumoto, S. (1996) DeNOx catalyst for automotive lean-burn engine. Catal. Today, 29, 43-45. 

One of the most straightforward methods to reduce carbon dioxide emissions is to enhance the fuel efficiency of engines. The three-way catalyst, although very successful at cleaning up automotive exhaust, dictates that engines operate at air-to-fuel ratios of around 14.7 1. Unfortunately, this is not the optimum ratio with respect to fuel efficiency, which is substantially higher under lean-burn conditions at A/F ratios of about 20 1, where the exhaust becomes rich in oxygen and NOx reduction is extremely difficult (Fig. 10.1). 

The most popular use of CSZ is as a gas sensor (2 sensor) for automotive exhaust, the structure of which is shown in Fig. 3.2. The sensor with the standard electrode (air) is inserted in exhaust pipes. The relation between the ratio of air to fuel (RAF) and the EMF is depicted in Fig. 3.3. The EMF shows a sharp drop at RAF = 15 (equivalent composition), left of which is called the rich burn region and right of which is called the lean burn region. Because the bad gases, such as CO and NO , , in exhausted gas are minimized at the point of equivalent composition, the value of RAF is controlled by the feedback of EMF. 

Gas sensors for automotive use, such as the X sensor, lean-burn sensor and sensors for car-room air-conditioning will be utilized more extensively. 

After the conquest of the second oil crisis, the trend of the automotive market turned and headed from low fuel consumption vehicles to high-grade and high-performance vehicles. As a result, the lean burn system with the limiting... 

The oxidation of HCs and CO requires an oxidizing atmosphere and the conversion of NO requires a reducing atmosphere. Thus a compromise has to be found to convert at least a main proportion of all three pollutants. The window of optimal operation is narrow and close to a lambda value of unity. At the end of the 1990s a new generation of automotive exhaust catalysts was developed, the NQr storage catalyst needed for lean burn engines. 

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