Combustion optimization for fuel economy improvement of a dedicated range-extender engine

Abstract

In this study, the combustion system of a dedicated range-extender engine was optimized based on a production engine for fuel economy improvement with the use of enhanced tumble flow, higher compression ratio, Atkinson cycle and exhaust gas recirculation (EGR). First, the shape of the intake port was optimized to improve in-cylinder tumble and turbulence for combustion enhancement. The computational fluid dynamics (CFD) results showed that compared to the original intake port, the peak tumble ratio during the compression stroke of the new port is improved by 74.0%, and the turbulent kinetic energy at the spark timing is increased by 33.0%, and the results were verified through the flow test bench experiment. The dyno experiment showed that, with the new intake port, the engine brake specific fuel consumption (BSFC) was improved for all test conditions. Then, the late intake valve closing (IVC) and a higher compression ratio were used in combination to adopt the Atkinson cycle. The IVC timing was set to 642° ATDC based on the preset power target. And the compression ratio was set to 12 to balance knock tendency and BSFC improvement. Finally, the cooled EGR was optimized to further suppress the knocking tendency to improve fuel consumption. The results showed that, with the cooling Strategy 2, the attainable maximum EGR ratio at 2400 rpm full load and 70 Nm conditions was increased, the spark timing could be significantly advanced, and the BSFC was improved. The improvement of BSFC is between 6 g/kW·h and 13 g/kW·h for the load range from 40 Nm to the full load. After the optimization, the minimum BSFC of the range-extender engine reaches 233 g/kW·h, while it is around 242 g/kW·h for the base engine. The operation area where fuel consumption is lower than 240 g/kW·h becomes much wider.

Prospects of Controlled Auto-Ignition Based Thermal Propulsion Units for Modern Gasoline Vehicles

“…The other pathway commonly used in internal combustion engines is positive ignition, most commonly spark ignition (SI). In CAI, the cylinder con-Energies 2023, 16, 3887 3 of 45 tents are relatively well-mixed, and if the post-compression pressure and temperature are sufficiently high, near-simultaneous AI is initiated at multiple points across the cylinder. This is different from traditional compression ignition (CI) 'diesel' combustion, where auto-ignition is spatially restricted to the vaporised fuel-air cloud around the fuel injector.…”

“…The emission reduction potential of HEVs can be bolstered by improving the fuel conversion efficiency of their TPUs and by reducing the associated pollutant emissions. Multiple avenues for TPU efficiency improvement are being actively researched, including ultra-lean combustion [12,13], fuel chemistry improvements [10], over-expanded cycles and flexible valve trains [14][15][16], waste heat recovery [17], alternative cycles [18], and advanced combustion concepts [19,20]. Novel TPU designs, such as micro-gas turbines [21] and free piston linear generators [22] are also being developed.…”

A numerical study on knock combustion suppression using targeted fuel injection in an SI engine

“…This dedicated engine adopted the Atkinson cycle and its CR was raised to 12.0 from 9.8 used in the original conventional engine. The details of the engine development and optimization can be found in Wu et al 29 and Meng et al 30 With the use of the Atkinson cycle, the engine's WOT output decreased to 9 bar IMEP at 2000 rpm due to the retarded intake valve closure timing. This operation point is one of the frequently used ones for electricity generation in the developed range-extender.…”

“…In spite of the reduced effective CR in the Atkinson cycle which is 10.6, the engine still exhibited high knock tendency at full loads. 29,30 Subsequently, the 2000 rpm and full load (9 bar IMEP) conditions were selected for the concept evaluation.…”