Book Description

Abstract : Fuel economy has become one of the top design parameters of modern passenger cars and light trucks. Recent CAFE regulations have required manufactures to push the fuel economy of US passenger vehicles under 8600 lb GVW beyond the limit of conventional technology [1]. In order to continue to meet the increasing requirements for fuel economy while still satisfying other design criteria including safety, tailpipe emissions, performance, and comfort, more expensive technology must be integrated into each vehicle specifically the powertrain. Diminishing returns of the payback period of fuel savings vs. higher initial vehicle cost has now become longer than the life of the vehicle. Because of this, the dollar per fuel economy benefit of each technology is being closely examined and investigated [1]. In this thesis, the potential fuel economy benefit of a technology was studied for feasibility and potential; the technology was on-board cylinder pressure sensors and the data available from them. Two low-cost cylinder pressure sensor types from two suppliers were evaluated and analyzed and compared to a laboratory sensor of known performance characteristics. Further the benefits from real-time cylinder pressure feedback capable of improving part load combustion phasing, combustion variability management were studied. Two areas of fuel consumption reduction which this thesis concentrates on are the improvement of locating spark advance through combustion duration feedback, and the extension of the dilute limit through combustion cycle stability measurement during transient operating conditions. By allowing the engine to run at more dilute conditions and locating spark advance to produce combustion durations closer to MBT, lower fuel consumption is possible. Vehicle EPA drive cycle data was used to examine areas of operation that were not operating at maximum efficiency to determine the fuel economy benefit that could be achieved through the availability of cylinder pressure data in terms of burn location and running dilute/lean. Methods to improve fuel economy in the engine such as dilution of air charge can have a negative effect on combustion stability [2]. In a laboratory environment combustion stability is measured during steady state operation using cylinder pressure data typically using a 100 cycle moving window for averaging. Transient engine operating conditions present in every drive cycle do not allow for calculating combustion stability in this way because it cannot be assumed that even two cycles are at the same operating conditions. If cylinder pressure sensor data were available on a production vehicle, the ability to measure combustion stability would exist but the transient measurement of combustion stability poses challenges which are discussed. A metric is developed to make comparable measurements in real time and the outcomes and benefits available from these measurements are evaluated.