Sharif Digital Repository

Some researches have been carried out in the last 20 years in order to increase the present IC engines thermal efficiency and their optimum performance. (HCCI) engine is viewed as a combination of spark-ignition (SI) and compression-ignition (CI) engines. This is because HCCI engines use premixed fuel/air mixture like SI engines and have auto ignition combustion after the mixture is compressed like CI engines. Control of combustion and ignition timing are the main challenges of these engines. Ignition delay, compression ratio, fuel air equivalence ratio and intake temperature and pressure are considered to be the most effective parameters on HCCI combustion.HCCI engines have great potentials... 

One strategy for increasing efficiency and decreasing brake specific fuel consumption in spark ignition engines is using variable valve timing mechanism which is proportional to engine speed and load. Variable timing refers to the opening and closing time of inlet and outlet valves and their duration and overlap. In conventional SI engines the performance of valves is designed on a fixed point at special engine load and speed. While investigations show that if performance time of valves is changed according to engine load and speed, performance parameters of engine will improve.
In reviewing articles related to variable valve timing, their effect was considered on volumetric efficiency.... 

The purpose of this study is to determine a function which estimate fuel/air equivalence ratio distribution inside combustion chamber of spark ignition engine for pollution minimization and maximum efficiency. To do this, we developed a code by which, we are able to model one SI engine cycle.
Seven distributions for fuel/air equivalence ratio were examined which include: Homogeneous, linearly decreasing, linearly increasing, sinusoidal increasing and decreasing, sinusoidal decreasing and increasing, cosinusodal decreasing, and cosinusodal increasing. The average fuel/air equivalence ratio for all of these distributions was 0.85.
The results for indicated power showed that,... 

In recent years, the idea of Homogenous charge compression ignition (HCCI) engines has been in the center of attention as a new generation of internal combustion engines. Intense decrease in pollutant emission rate like NOx, low fuel consumption and high thermal efficiency are the main reasons of why these engines are in center of attention, however, some drawbacks, which the main one combustion control which happens in limited operation range between knock and misfiring has limited the use of these engines. Hence approaches like adding synthesis gas, using exhaust gas recirculation, controling effective comperession ratio by using variable valve timing, changing the input conditions... 

CFD models are accurate but time-consuming for simulation and optimization of steam methane reformer and controlling the tube wall temperature, and syngas production rate and unsuitable for online optimization. Empirical data-driven models are less accurate when there are wide variations in operating conditions. The physics-based model presented in this thesis overcomes these limitations. In this model, the furnace side and the process side are divided into zones with uniform temperature and composition, and for each zone, mass, energy and momentum balances are derived. Radiative heat transfer modeling and calculation of exchange areas are accomplished with the zone method. The system of...