This week's talks are on:
Abstract: A potential pathway to efficiency gain in a CI combustion is to avoid the limitation of, in cylinder high temperature, as it is a significant enabler to heat transfer losses and NOx/soot formation. This high temperature entails a diffusion-driven combustion with large burn rate. Isobaric combustion is proven to burn similar diffusion combustion but with a lower in cylinder temperature, in comparison to conventional diesel combustion (CDC) with comparable efficiency and emissions. In this study, fuels with high octane ratings are considered to provide further understanding on isobaric combustion utilizing Primary Reference Fuel (PRF) in a heavy duty CI engine of single injector setup, with multiple injection strategies. The fuel flow rate of each injection of a four injection strategy is reproduced and characterized by high pressure fuel pump test rig equipped with a piezoelectric pressure sensor to measure the spray momentum force. Measurement of injection rate and mass for each fuel also aids the development of isobaric combustion modeling. The study is focused to demonstrate the role of fuels on isobaric rate of heat release (RoHR) from low to high load conditions. With diesel fuel, isobaric combustion is initiated with the 1st injection irrespective of loads. In contrast, fuels like isooctane exhibit distinct start of ignition. At low loads, the 1st and 2nd injections are ignited by the 3rd injected spray with extended premixing process resulting in partial premixed combustion (PPC) at 50 bar. With 70 bar case, combustion is initiated by the 2nd spray while the 3rd and 4th injections are a typical diffusion combustion regime similar to CDC. Boosting toward intermediate loads, Isooctane has the advantage to advance start of injection to overcome the large burn rate associated with diesel. Whereas diffusion controlled combustion is realized at high loads with ignition of the 1st injection. At high loads, the in cylinder temperature and pressure are 850 K and 150 bar respectively which allow to phase combustion of isooctane with the 1st injection similar to diesel fuel at these conditions but with improvement on NOx/soot emissions and comparable gross indicated efficiency.
Bio: Bassam Aljohani is a PhD student of Mechanical Engineering Program supervised by Prof William Roberts. Bassam’s received his Master’s from Northeastern University with thesis supervised by Prof Hameed Metghalchi. Before that, he received his BSc from Pennsylvania State University through Taibah University “3+1”scholarship program. Research interests include multiple injection strategy to enable fuel flex of high-pressure combustion in CI engines.
Abstract: Engine knock is an abnormal combustion phenomenon that limits the thermal efficiency and service life of spark-ignition engines. A better understanding of the knock mechanisms and characteristics is beneficial to knock alleviation and engine efficiency improvement. In this study, a metal liner with four evenly-spaced spark plugs in the periphery of the combustion chamber is designed to initiate knock from different positions. Four spark strategies are applied to the single-cylinder optical research engine and six pressure sensors are utilized to analyze the local pressure oscillations in the cylinder. The knocking combustion is investigated by simultaneously 72 kHz high-speed imaging and 6-point pressure sensing. The experimental results indicate that using multiple spark-ignition could promote knock intensity, advance the start of auto-ignition and introduce more acoustic resonance modes. Natural flame luminosity analysis demonstrates that the initial auto-ignition sites only cause weak pressure oscillations, and the instantaneous combustion of the remaining end-gas increases the heat release rate significantly and gives rise to more violent pressure oscillations. The end-gas resides in the gaps among the flame fronts generated by different spark strategies while the first auto-ignition sites are not evenly distributed in the end-gas zone. This fact gives insights into the local temperature non-uniformity of the end gas zone that affects the spatial distributions of the initial auto-ignition sites in the cylinder.
Bio: Hao Shi joined KAUST from 2017 after finishing his master study from Huazhong University of Science and Technology in China, and he is currently a PhD student in the internal combustion engine group in CCRC. He has strong interests on the fields of high efficiency engine combustion technologies, and his current researches are mainly focused on engine knock study and partially premixed combustion (PPC) with optical diagnostic and related techniques, such as laser ignition, planar laser-induced fluorescence (PLIF), natural flame luminosity (NFL) with high speed imaging, and so forth.