Holy Grail for ICE engines ! Homogeneous Charge Compression Ignition (HCCI) Engine
HCCI is the ultimate combustion method for achieving both CO2 reduction and clean exhaust using auto-ignition of gasoline, as in a diesel engine. Nissan is developing this technology for commercial use.
The system features lower-temperature combustion compared to ordinary gasoline engines, resulting in nearly no NOx emissions. It offers the highest potential heat efficiency among internal-combustion engine systems, leading to projections of major cuts in CO2 emissions. Current HCCI technology allows only a limited range of stable combustion, and expanding that is the challenge ahead.These benefits are due to the auto-ignition process of the dilute mixture of fuel and air during compression.
Control Problem :-
However, because there is no direct ignition trigger, control of ignition is inherently more difficult than in standard internal combustion engines. This difficulty necessitates that a feedback controller be used to keep the engine at a desired (efficient) setpoint in the face of disturbances. Because of the nonlinear autoignition process, the sensitivity of ignition changes with the operating point. Thus, gain scheduling is required to cover the entire operating range of the engine. Controller tuning can therefore be a time intensive process. With the goal of reducing the time to tune the controller, an extremum seeking (ES) to tune the parameters of various forms of combustion timing controllers. Additionally, in this dissertation it is demonstrated how ES can be used for the determination of an optimal combustion timing setpoint of an experimental HCCI engine. The use of ES has the benefit of achieving both optimal setpoint (for maximizing the engine efficiency) and controller parameter tuning tasks quickly. The lack of a direct combustion trigger makes control of combustion timing during transients especially challenging. To aid in HCCI engine control during transients, we have developed a model that can be used to derive a controller for a thermally-managed, gasoline and natural gas fueled HCCI engine. The model uses an ignition threshold derived from detailed chemical kinetic simulations of HCCI engine combustion to provide an estimate for the combustion timing. The ignition threshold is a function of both temperature and pressure. An estimate of the residual gas fraction from the previous cycle can also be obtained, which is essential information due to the strong temperature sensitivity of HCCI ignition. This model allows the synthesis of nonlinear control laws, which can be utilized for control of an HCCI engine during transients.