Preliminary Testing of n-Butanol HCCI on High Compression Ratio Diesel Engines 2019-01-0577
The control of combustion phasing in homogeneous charged compression ignition (HCCI) combustion is investigated with neat n-butanol in this work. HCCI is a commonly researched combustion mode, owing to its improved thermal efficiency over conventional gasoline combustion, as well as its low nitrogen oxide (NOx) and particulate matter emissions compared to diesel combustion. Despite these advantages, it lacks successful widespread implementation with conventional fuels, primarily due to the lack of direct combustion phasing control. However, with the use of alternate and renewable fuels, such as n-butanol, the unique fuel properties present advantages in terms of auto-ignition characteristics. In this preliminary study, chemical kinetic simulations are conducted to study the autoignition characteristics of n-butanol under varied background pressures, temperatures, and dilution levels using established mechanisms in CHEMKIN software. Increasing the pressure or temperature led to a shorter ignition delay, opposing the trend observed of increasing the dilution (or EGR) levels. These ignition delay simulation results are used as a guide for the experimental study of n-butanol HCCI combustion on engine tests. Experiments are conducted near mid-engine load (~6 bar IMEP) using two high compression ratios, 16.2:1 and 18.2:1. Throughout the experimental tests, a few controllable parameters are swept to examine their respective effects on the combustion; intake air temperature, pressure and oxygen levels. Intake air temperature can be controlled through a heater installed to the intake air manifold. Exhaust gas recirculation (EGR) is implemented to achieve the desired intake oxygen levels. At a CR of 16.2:1, achieving desired combustion timing is not possible by the sole manipulation of boost. A combination of intake boost and heating is used to achieve stable combustion. At a CR of 18.2:1, boost alone is sufficient to reach target loads, however the pressure rise rate reaches significant high points when reaching the optimal CA50 timing. To help regulate this limit, EGR is implemented to improve combustion stability.
Simon Leblanc, Prasad Divekar, Xiaoye Han, Jimi Tjong, Tie Li, Ming Zheng
Univ of Windsor, Shanghai Jiao Tong Univ