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Development of a Gasoline Direct Injection Compression Ignition (GDCI) Engine
Abstract:
In previous work, Gasoline Direct Injection Compression Ignition (GDCI) has demonstrated good potential for high fuel efficiency, low NOx, and low PM over the speed-load range using RON91 gasoline. In the current work, a four-cylinder, 1.8L engine was designed and built based on extensive simulations and single-cylinder engine tests. The engine features a pent roof combustion chamber, central-mounted injector, 15:1 compression ratio, and zero swirl and squish. A new piston was developed and matched with the injection system. The fuel injection, valvetrain, and boost systems were key technology enablers.
Engine dynamometer tests were conducted at idle, part-load, and full-load operating conditions. For all operating conditions, the engine was operated with partially premixed compression ignition without mode switching or diffusion controlled combustion. At idle and low load, rebreathing of hot exhaust gases provided stable combustion with NOx and PM emissions below targets of 0.2g/kWh and FSN 0.1, respectively. The coefficient of variation of IMEP was less than 3 percent and the exhaust temperature at turbocharger inlet was greater than 250 C. BSFC of 280 g/kWh was measured at 2000 rpm-2bar BMEP. At medium-to-higher loads, rebreathing was not used and cooled EGR provided NOx, PM, and combustion noise below targets. MAP was reduced to minimize boost parasitics. At full load operating conditions, near stoichiometric mixtures were used with up to 45 percent EGR. Maximum BMEP was about 20 bar at 3000 rpm. For all operating conditions, injection quantities and timings were used to control mixture stratificaton and combustion phasing.
Transient co-simulations of the engine system were conducted to develop control strategies for boost, EGR, and intake air temperature control. Preliminary transient tests on a real engine with high rate of load increase demonstrated potential for very good control. Cold start simulations were also conducted using an intake air heating strategy. Preliminary cold start tests on a real engine at room temperature demonstrated potential for very good cold starting. More work is needed to calibrate the engine over the full operating map and to further develop the engine control system.