Stanford team develops model and controller for reducing HCCI cycle-to-cycle variation
30 November 2014
A team led by researchers from Stanford University has developed a simplified, discrete-time analytical model of homogeneous charge compression ignition (HCCI) dynamics. The model forms the basis for the design of a simple controller that reduces combustion timing variations in simulation.
Late-phasing homogeneous charge compression ignition operating conditions have the potential to expand the useful operating range of homogeneous charge compression ignition in internal combustion engines. However, significant combustion instabilities can occur at late-phasing operating conditions. Combustion phasing and work output variations at these conditions are characterized by a pattern in which the combustion phasing alternates between being earlier than the desired timing and later than the desired timing.—Jungkunz et.al
The team traced the characteristic to a negative eigenvalue in the model.
Experimental results showed the controller successfully reducing the cyclic variations in combustion by altering the exhaust valve timing, resulting in stable combustion and an expanded operating range.
Adam F Jungkunz, Nikhil Ravi1, Hsien-Hsin Liao, Stephen M Erlien, J Christian Gerdes (2014) “An analytical method for reducing combustion instability in homogeneous charge compression ignition engines through cycle-to-cycle control,” International Journal of Engine Research doi: 10.1177/1468087414557052
This is a significant advance in technology.
HCCI operation improves the Internal Combustion engine in both its Otto and Diesel variants.
Producing an Otto engine as fuel efficient as a Diesel, while allowing a much light weight diesel engine design, while in mostly CI diesel operation, achieves better fuel efficiency than either.
It approaches the theoretical maximum of IC fuel efficiency.
The typical Diesel engine is 200-600 Lbs heavier than an OTTO cycle equivalent. Removing 3-400 Lbs from a car's weight is very important to fuel economy. Plus it still achieves the fuel efficiency of diesel operation; and more economy by the weight reduction, is something all automakers covet.
Posted by: D | 02 December 2014 at 03:21 PM