The Potential Of Methanol As An Alternative Fuel For Heavy Duty Engines PDF Download

The emission of carbonaceous particulate matter (soot) from work-producing devices is a global problem. Direct-injection, compression-ignited (Diesel) engines are a source of soot emissions that are problematic because they are mobile and operate regularly within populated regions. The subsequent effect on air quality is a serious health concern due to their small size and potential penetrability within the human body through the lungs. Furthermore, their contribution to atmospheric aerosols has a significantly negative effect on the environment. The problem with Diesel engine combustion is primarily a function of the fuel properties and subsequent combustion kinetics. The attraction of No.~2 Diesel fuel is that it is easily autoignitable, and for a typical direct-injection, compression-ignited engine this is a desirable quality. By employing a high-temperature combustion strategy, however, a host of alternative fuels become viable. This work addresses the prospects for using non-traditional fuels within a direct-injection, compression-ignited engine. A number of alternative fuels are identified as having potential, namely methanol, ethanol, butanol, dimethyl ether, synthesis gas, and methane (as a surrogate for natural gas). These are attractive because they are either oxygenated (and rely less on ambient gas entrainment) or gaseous (and can turbulently mix with ease). The combustion behavior of each fuel is examined by two means: First, a simple and well-controlled apparatus allows single-jet combustion to be imaged with a high-frame-rate, color digital camera. Second, a computationally efficient, quasi-dimensional jet model is used to explore each fuel with a detailed chemical mechanism, and includes a multi-step soot model. Once each fuel is examined independently, a subset are identified as forming too much soot such that their use within a production engine would emit levels above the EPA regulation standard. Two separate soot reduction methods are then explored within this work: dilution of the fuel with water, and dilution of the ambient gas with exhaust gas species. For each strategy, images are obtained that provide direct evidence of reduced soot formation. The jet model is then examined in detail to gain deeper insight into the potential mechanisms leading to the observed soot reduction.