The Axially Stratified-Charge Engine: Control, Calibration, and Vehicle Implementation 851674

The axially stratified-charge (ASC) concept was demonstrated in a compact production car by modifying the engine and developing the required control system and calibration. Two production 1.8 L four-cylinder engines were modified to operate as ASC engines by adding shrouded inlet valves to produce swirl, and by providing timed-sequential port fuel injection. One of these engines was calibrated for minimum fuel consumption in the laboratory using a computer-controlled engine and dynamometer. The second engine was installed in a vehicle equipped with an oxidizing catalyst. A complete control system was developed for this engine to implement the minimum fuel consumption calibration in the vehicle. The fuel economy of the ASC vehicle was six percent better than that of the base vehicle. It had acceptable driveability, and had a 91 Research octane requirement on the fuel. Tailpipe exhaust emissions of the ASC engine vehicle using only an oxidizing catalyst were 0.39 g/mile HC, 1.7 g/mile CO, and 0.87 g/mile NOX, which are below the 1984 Federal emission standards.
THIS PAPER PRESENTS THE RESULTS of a project to demonstrate the axially stratified-charge (ASC) engine in a vehicle. A previous study (1)* suggested the potential for achieving low NOX emissions and improvements in fuel economy by operating the ASC engine either at leaner air-fuel ratios or with more exhaust gas recirculation (EGR) than conventional engines. The higher EGR tolerance of the ASC engine in dynamometer tests resulted in a substantial (78 percent) reduction in engine-out NOX emissions, thus providing the possibility of controlling NOX without a reducing catalyst, while using an oxidizing catalyst to reduce HC and CO emissions in the exhaust. A brief review of the method used to stratify the fuel-air mixture along the cylinder axis is given below. Figure 1 shows the sequence of events that lead to axial stratification of the charge with the richest mixture near the top of the combustion chamber and the leanest mixture near the piston top. Basically the concept works as follows: air is inducted during the early part of the intake stroke (Fig. 1(a)); a shrouded inlet valve imparts swirling motion to the air entering the cylinder; the fuel is injected in a short burst during the latter part of the intake stroke so that the last part of the injected fuel enters the cylinder just before the inlet valve closes (Fig. 1(b)); the mixture is then compressed and ignited (Fig. 1(c)). The swirling motion of the charge preserves stratification along the cylinder axis during the compression stroke. More detailed accounts of the concept, its benefits, its experimental validation in a single-cylinder engine, and its application in multicylinder engines have been reported (1, 2 and 3). In two recent papers (4-5) a lean combustion system has been described, which appears to operate on the axially stratified-charge principle (6), and demonstrates the benefits expected of this engine when operated lean.


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