Cylinder deactivation is a fuel consumption reduction technology for throttled internal combustion engines and other engines with thermal efficiency loss at part cylinder load. Recent production implementations, deactivating fixed sets of cylinders under part-load operating conditions, have had limited "fly zones" due to issues with drivability and noise, vibration and harshness (NVH). Dynamic skip firing, which in its ultimate form incorporates anytime, any-cylinder deactivation, continuously varies the number of firing cylinders, along with cylinder load, obtaining flexible control of acoustic and vibrational excitations from the engine, and allowing an expanded operational envelope with fewer drive ability/NVH issues. This paper outlines design considerations of dynamic skip fire operational strategies, discusses implementation of the system on a vehicle, and presents benefits to fuel economy and NVH.
We examine the use of in-cylinder measurements for engine control, with emphasis on emissions control during cold start. First, the cold start emissions control problem is described. An overview of previous research in the area of in-cylinder measurements for control is presented, including sensors for pressure and other quantities. Next, analysis of cylinder pressure is described. Lastly, a coldstart engine test stand, and preliminary experimental tests of cylinder pressure measurement and realtime processing are presented.
The initial 1-2 minutes of operation of an automotive spark-ignition engine, commonly called as the "coldstart" period, produces more than 75-80 % of the hydrocarbon (HC) emissions in a typical drive cycle. Model-based controller development requires accurate, yet simple, models that can run in realtime. Simple, intuitive models are developed to predict both tailpipe hydrocarbon (HC) emissions and exhaust temperature during coldstart. Each of the models is chosen to be sum of first order linear systems based on the experimental data and ease of parameter identification. Inputs to these models are AF R, spark timing and engine crankshaft speed. A reduced order thermodynamic model for the catalyst temperature is also developed. The parameters are identified using least squares technique. The model estimates for the coldstart are compared with the experimental results with good agreement.
A method of lean air-fuel ratio control using combustion pressure measurement Lee, Albert T.; Wilcutts, Mark; Tunestål, Per; Hedrick, J. Karl General rights Copyright and moral rights for the publications made accessible in the public portal are retained by the authors and/or other copyright owners and it is a condition of accessing publications that users recognise and abide by the legal requirements associated with these rights.• Users may download and print one copy of any publication from the public portal for the purpose of private study or research.• You may not further distribute the material or use it for any profit-making activity or commercial gain • You may freely distribute the URL identifying the publication in the public portal Take down policy If you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately and investigate your claim. AbstractIn this paper a method for control of air-fuel ratio (AFR) in cold or lean-burning spark-ignited engines is investigated. The technique uses combustion pressure as measured by a cylinder-mounted sensor, and is based on the phenomenon of increasing cycleto-cycle combustion pressure variation as the air-fuel mixture approaches the limits of flammability. The cylinder pressure is measured from one engine cycle to the next, and large drops in mean effective pressure (IMEP) are used as an indicator of poor combustion. In response, the airflow or fuel flow to the engine can be manipulated. In a series of experiments, the air and fuel are alternately investigated as control inputs, and performance compared. The resulting control system is a high-bandwidth AFR control strategy that can be used under cold or lean conditions when conventional exhaust gas oxygen sensor cannot be used. Moreover, the method is directly tied to the combustion process and the relevant performance measure F combustion stability F that is perceptible to the driver as a rough-running engine. r
Dynamic skip fire is a control method for internal combustion engines in which engine cylinders are selectively fired or skipped to meet driver torque demand. In this type of engine operation, fueling, and possibly intake and exhaust valves of each cylinder are actuated on an individual firing opportunity basis. The ability to operate each cylinder at or near its best thermal efficiency, and to achieve flexible control of acoustic and vibrational excitations has been described in previous publications. Due to intermittent induction and exhaust events, air induction and torque production in a DSF engine can vary more than conventional engines on a cycle-to-cycle basis. This paper describes engine thermofluid modeling for this type of operation for purposes of air flow and torque prediction. Development of a one-dimensional model of medium complexity is described, along with solutions for practical issues encountered with the standard configuration of onedimensional simulation packages such as GT-SUITE. Airflow dynamic and thermodynamic simulation results for skip fire engine operation are presented and compared with experimental data under several different firing sequences. The dependence of air charge and net indicated mean effective pressure on skip fire sequence is illustrated. Finally, a method of air estimation compensation is described via characterization of each induction event by skip history, both of the particular cylinder as well as previous cylinders in the firing order.
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