Access Type
Open Access Dissertation
Date of Award
January 2024
Degree Type
Dissertation
Degree Name
Ph.D.
Department
Mechanical Engineering
First Advisor
Naeim Henein
Abstract
In future, compression ignition engines are anticipated to continue powering heavy-duty trucks and certain machinery, while passenger vehicles and light-duty vehicles will increasingly be battery powered. However, compression ignition engines face challenges such as combustion instability, misfiring, and high unburnt hydrocarbon emissions when started under severe cold conditions. These issues can be mitigated through the use of real-time feedback to the engine's control module.
The ion current signal, reflective of combustion and emissions characteristics, has proven to be a reliable feedback signal under warmed-up conditions. In this dissertation, the potential of the ion current signal as a feedback mechanism during cold start and cold idling was investigated. To study the ion current signal, cold starting experiments were conducted using ULSD in a VW’s 2.0-liter, direct injection, 4-cylinder compression ignition engine at ambient temperatures of -10 ⁰C, 0 ⁰C, 10 ⁰C, and 20 ⁰C. It was observed that at lower ambient temperatures, the ion current peak could sometimes be too small and disguise as noise. In some misfiring cycles, the ion current was detected even though the pressure trace did not exhibit a combustion event, indicating that autoignition occurred but combustion failed to sustain. In firing cycles, an ion current characteristic could reasonably predict combustion phasing at higher ambient temperatures. These findings suggest that the ion current signal could provide valuable feedback to mitigate cold-starting problems in compression ignition engines.
Un-sustained combustion in some engine cycles can be attributed to poor equivalence ratio distribution in the fuel-air mixture. Hence, a novel methodology was developed to evaluate whether the quality of the fuel-air mixture is sufficient to sustain combustion and prevent misfiring. This methodology is based on 3D CFD simulations of fuel spray and does not require chemical kinetic calculations. As a result, its key advantage lies in its computational cost-effectiveness, while it also takes the engine geometry into consideration. However, this methodology is semi-empirical, as it relies on insights from a separate set of cold starting experiments conducted in the same engine. ULSD was utilized in these experiments as well, and a two-injection strategy was deployed at an approximate ambient temperature of 22.5 °C, a condition under which the glow plug remained inactive. The key insight gained was that the engine misfired when the fuel-air mixture from the pilot injection became too lean or did not have enough time to autoignite before merging with the main fuel-air mixture. Therefore, the methodology evaluates whether the quality of the pilot fuel-air mixture and the time it requires to autoignite are above certain thresholds determined in this work. Lastly, the methodology was observed to fall short when the glow plug was active in a cold-starting experiment. Hence, a modification to the methodology was proposed that would be effective whenever the glow plug is active. Although ULSD was utilized to develop the methodology, it can be adapted for low-carbon intensity fuels such as renewable diesel, hydrogen, biodiesel, etc., which are poised to be the fuels of the future.
Recommended Citation
Trivedi, Manan Jyotin, "Ion Current Analysis And Misfire Prediction During Cold Start In A Compression Ignition Engine" (2024). Wayne State University Dissertations. 3981.
https://digitalcommons.wayne.edu/oa_dissertations/3981
