Initial Characterization of an Improved Diesel Combustion Chamber

Many drivers and pedestrians are familiar with the nuisance of “coal rolling,” where a modified diesel truck spews a cloud of black soot from its exhaust. Coal rolling is an extreme example of combustion inefficiency in an engine, where deliberate incomplete combustion of the fuel leads to sooty exhaust. Even in real use cases, combustion inefficiency can lead to higher fuel consumption and health and environmental concerns from soot and other incomplete combustion products.

Despite the many improvements in diesel combustion since the first diesel engines 130 years ago, they still represent the most efficient road-transportation powertrain available and still have possible efficiency gains. Studying reacting fuel sprays in specialized test facilities, with kilohertz speed imaging allows for time- and space-resolved data of individual combustion events. A suite of different optical diagnostic techniques, 1) schlieren (density-sensitive), 2) OH* chemiluminescence (chemical reaction-sensitive), and 3) two-color pyrometry (soot temperature-sensitive) allows study of the fundamental mixing and ignition processes.

A new constant pressure flow rig (CPFR) at the University of Alabama Engines and Combustion Lab (UA ECL) has recently been constructed that can emulate engine conditions by reaching the temperatures and pressures present in modern diesel engines (1000 Kelvin, 100 bar) and enables collection of statistically significant data sets on the order of hundreds or thousands of injections.

Being a new experimental apparatus, it must be characterized and verified with the data from the past literature. The ECL has taken this as an opportunity to improve various other aspects of working with the chamber, such as spatially aligning the video data from various cameras, reducing data analysis run time by 40-50%, designing a new model for the thermodynamic properties, and updating control and calibration software. This paper represents the first use of these new capabilities.