Investigating Pre-Mixed Charge Compression Ignition Combustion in a High Compression Ratio Engine

Utilizing a higher compression ratio in a Compression Ignition (CI) engine grants an obvious advantage of improved thermal efficiency. However, the resulting combustion temperatures promote dissociation ensuing in increased nitrogen oxide (NO_x) emissions. Unfortunately, due to the inherent properties of CI combustion, it is difficult to achieve simultaneous reduction of NO_x and particulate matter (PM) through conventional combustion methods. Taking a different route though accomplishing Homogeneous Charge Compression Ignition (HCCI) in CI engines will largely eliminate NO_x and PM; however, combustion can result in a significant increase in hydrocarbon (HC) and carbon monoxide (CO) emissions due to the low volatility of diesel fuel. Hence, this work attempts another avenue of Low Temperature Combustion (LTC) by employing Pre-mixed Charge Compression Ignition (PCI) combustion on a comparatively higher compression ratio (21.2) single cylinder CI engine. An injection timing sweep was conducted using a common rail injection system with a 6-hole nozzle injector. Exhaust emissions were monitored using a Fourier Transform Infrared Spectroscopy device and Smoke Meter to analyze the extent of the NO_x-PM trade-off along with both HC and CO emissions. Finally, a fuel injection quantity sweep with the fuel injection timing fixed at 60° Before Top Dead Center (BTDC) and 100° BTDC was performed to determine the maximum amount of fuel that may be injected early in the compression stroke without a significant growth in the heat release due to combustion. As the power generated was comparatively lower at advanced fuel injection timings, thermodynamic calculations and a heat release program were utilized to comprehend the magnitude of combustion.