ABSTRACT :

Combustion of fuel with an oxidizer in an IC Engine generates significant amount of mechanical energy but results in product gases that are harmful for the environment. The energy produced and the pollutant gases formed while operation of any engine depend on several factors such as fuel characteristics, geometry of the combustion chamber and operating conditions.
Among the two common types of IC engine, compression ignition (CI) engines are preferred in many applications due to high thermodynamic and mechanical efficiency. Several studies were performed in previous few years to determine the CI engine performance and to quantify the gases released as a result of air-fuel reaction. A detailed analysis, however, for the effect of the many major parameters/factors on flow distribution, temperature and species concentration variation was not carried out. The reasons were the complexity of the case which includes dynamic mesh along with the combustion phenomenon and non-availability of the adequate computational resources.
As the fossil fuels are being gradually exhausted, it provides sufficient motivation to investigate an alternate fuel like biodiesel as a replacement for CI engine fuel. This thesis thus aims to provide insight into the fluid dynamics within the direct injection CI engine cylinder and predict engine emission characteristics using biodiesel. This computational study utilizes a single step combustion reaction mechanism and reveals flow behavior of air-diesel and air-biodiesel mixtures in terms of velocity profiles, swirl and tumble ratios. The computations for NOx formation are also performed and the results show that the relative NOx mass fraction are 1620 and 1270 using diesel and biodiesel, respectively.
Another significant parameter investigated is the orientation of fuel injector in CI engines. The computer simulations show that temperature values are high when fuel injection angle is large. For example, the time-averaged maximum temperature reaches up to 1442 K when the fuel injector angle is 72°, but when the injector angle is 24°, the temperature reduces to 1250 K. NOx mass fraction is also found to be lowest with this injector orientation. Based on the findings of temperature and emissions, it is suggested that moderate fuel injector angles (24°--40°) can be considered suitable for the CI engines. The fluid pressure obtained through CFD at different crank angles and pollutant concentrations are also compared with experiments. The difference of results is mostly within 20% which indicates reliability of the computational work.
The application of the approach is demonstrated on a 738 cc 4-stroke single cylinder direct injection CI engine but it is equally valid for other engines, provided the

engine dimensions are incorporated. The procedure can be extended to other types of engines and other fuels in order to explore different engines, combustion and emission performance.