Diesel Engine Emissions During High EGR Operation

Due to their high fuel economy, diesel engines are widely used in on-road applications. The need to maintain efficiency and performance while meeting increasingly stringent emissions regulations is forcing engine developers to design advanced in-cylinder combustion strategies tailored to minimize emissions and maximize performance at specific operating conditions. These strategies are currently limited by high emissions and poor performance as the engine's speed and load change during transient operation. Even under a wide range of steady-state combustion conditions, there is a shortage of fundamental understanding of the effects of the engine load, charge conditions and charge composition on the combustion process.Transient tests provide information on the effects of a change in the operating mode of an engine. The results of such tests are highly specific to the engine, air exchange, and control system used; it can also be difficult to identify cause and effect relationships relating to the combustion event. As a result, while such tests are necessary for engine development, they do not provide the information needed to develop the improved fundamental understanding being sought in this project. Therefore, this project will adopt well controlled steady-state engine tests with the operating conditions selected to be representative of the charge conditions encountered by individual engine cycles during transient operation. Cycle-to-cycle variability in the composition of the air in the intake and exhaust streams will be measured and will be compared to the observed variability in the combustion event. A variety of tests, including the use of an ignition promoter, will permit evaluation of the principal causes of combustion instability.Combustion instability leads to poor engine performance and high unburned fuel emissions. It is one of the key barriers to the application of high EGR strategies to control diesel engine emissions. Many new diesel engine injection systems have the potential to inject fuel several times within one combustion cycle. This project will use the newly developed fundamental understanding of high-EGR operation to identify novel injection strategies that can improve combustion performance. An optimization process will be used to identify the most promising potential strategies over a range of engine operating conditions similar to those encountered during transient operation. This project will involve two PhD research students (one of whom will be funded by Loughborough University) working under the close supervision of the PI. An advisory panel composed of experienced academic and industrial engine researchers will provide guidance for the project. Technical support will be provided by skilled research technicians. The research will be conducted on a newly installed, state-of-the-art automotive-sized single-cylinder research engine. The overall project methodology will involve first identifying the operating conditions which will be encountered during a transitional mode-shift between low temperature (high EGR) and conventional (low EGR) diesel combustion. Then, steady-state engine tests will be conducted over a range of conditions which are representative of the charge composition and EGR levels encountered during transient operation. Based on these experimental results, those operating conditions which demonstrate high emissions and/or poor combustion stability will be investigated in more detail, including optical in-cylinder evaluation and cycle-resolved emissions measurements. A combustion enhancer will be used to investigate the effects of kinetic limitations at high EGR levels. Finally, a range of multiple-injection strategies will be evaluated to identify techniques for controlling emissions under high-EGR transient operation.