The Potential of a New Type of Carburetor to Assist SORE in Meeting EPA/CARB Phase 3 Legislation

摘要

Small off-road engines (SORE) have been recognized as a major source of air pollution. It is estimated that non-hand-held SORE annually produce over 1 million tons of HC+NO{sub}x and over 50 million tons of CO{sub}2. The fuel system design and its operating AFR are of key importance with regard to engine operation and engine-out emissions. The conventional low-cost float carburetors used in these engines are relatively ineffective at atomizing and preparing the fuel for combustion requiring a rich setting for acceptable functional performance. EPA and CARB have confirmed that Phase 3 limits are achievable for a "durable" engine fitted with a conventional well calibrated and manufactured "stock rich setting" float carburetor together with catalytic oxidation after-treatment and passive secondary air injection. The EPA and CARB strategy for meeting Phase 3 only considers the use of conventional float carburetors that operate at rich AFR's over their entire engine operating range as no other cost-effective alternative fuel system is yet available on the market. A cost-effective alternative to the conventional carburetor that enabled leaner or optimized AFR operation with load and improved combustion performance would open the door to alternative strategies to meeting the phase 3 limits. This paper presents a completely new form of mechanical carburetor that gives AFR control with load, improved mixture preparation for improved combustion performance and has a lower production cost than conventional carburetors. The conventional and new fuel system designs and operation are discussed in detail and their technical merits demonstrated in the form of engine test data. The performance of different after-treatment systems is also simulated for different AFR profiles with load for a conventional or unmodified SORE engine. With optimized leaner operation and improved combustion characteristics, this new carburetor technology can provide significant engine-out CO and HC+NO{sub}x reductions on the J1088 test cycle without loss of functional performance. Depending on the chosen emissions control strategy, minimum engine-out emissions or optimum engine AFR for oxidation or three-way after-treatment or another, this new carburetor technology can be easily calibrated to provide the desired engine-operating AFR profile on the J1088 cycle.