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Today, homogenous charge compression ignition (HCCI) engines are becoming very popular because of their potential to reduce soot and nitric oxides (NOx) emissions simultaneously. But, their performance and emission characteristics are very much dependent upon fuel injection strategy and parameters. However, they also have many challenges viz., improper combustion phasing, high rate of pressure rise and narrow operating range. Therefore, addressing them is very essential before making them a commercial success. This study focuses on evaluating the effect of fuel injection strategy and parameters on the performance and emission characteristics of a HCCI engine by computational fluid dynamics (CFD) analysis. In this study, a four-stroke engine operating in the HCCI mode is considered and the CFD analysis is carried out by using the CONVERGE.

In-cylinder air motion in an internal combustion (IC) engine has a strong influence on engine combustion, performance and exhaust emissions. In spark ignition engines, large-scale in-cylinder fluid flows like swirl and tumble generated during intake stroke will be later dissipated as turbulence during compression stroke before ignition which promotes flame kernel growth and propagation rate. These types of in-cylinder flows are more desirable in stratified and direct injection spark ignition engines. In IC engines, in-cylinder flows are mainly affected by shape of combustion chamber, intake manifold orientation, compression ratio, crank angle position and engine speed.

In the present work, an attempt was made to study numerically, using CFD, the effect of vane-shape on the flow-field and heat transfer characteristics of a disc brake rotor for different configurations and at different speeds. Initially, the CFD code used in this work was validated by experimental results obtained by conducting experiments on a test rotor using particle image velocimetry (PIV). Further, six types of rotor configurations viz., straight radial vane (SRV), tapered radial vane (TRV), modified tapered radial vane (MTRV), circular pillared (CP), diamond pillared (DP) and modified diamond pillared (MDP) were considered for the numerical analysis. Three of them were radial type and other three were of pillared type rotors. A rotor segment of 20° was considered for the numerical analysis due to rotational symmetry. Validation was done for SRV rotor, for which the experimental and predicted results were in good agreement.

The homogeneous charge compression ignition (HCCI) engines emit low levels of smoke and NOx emissions. However, control of ignition, which is mainly controlled by fuel composition, the equivalence ratio and the thermodynamic state of the mixture, is a problem. In this work, acetylene was as the fuel for operating a compression ignition engine in the HCCI mode at different outputs. The results of thermal efficiency and emissions have been compared with base diesel operation in the (compression ignition) CI mode. The relatively low self ignition temperature, wide flammability limits and gaseous nature were the reasons for selecting this fuel. Charge temperature was varied from 40 to 110°C. Thermal efficiencies were almost equal to that of CI engine operation at the correct intake charge temperature. NO levels never exceeded 20 ppm and smoke levels were always lower than 0.1 BSU. HC emissions were higher and were sensitive to charge temperature and output.

This paper deals mainly with computer simulation of processes of Gasoline Direct Injection (GDI) associated with Extended Expansion Engine (EEE) concept applied to a four-stroke, single-cylinder SI engine. In the case of standard SI engines, part-load brake thermal efficiencies are low due to higher pumping losses. The pumping losses can be reduced by operating the engine always at full throttle as done in extended expansion engine. In extended expansion engine, higher Geometric Expansion Ratio (GER) compared to Effective Compression Ratio (ECR) is responsible for better performance at part loads. Usually, in this engine, by delaying inlet valve closure timing along with reduced clearance volume, extended expansion is achieved. Experimentally many researchers have proved that variable valve timing and variable compression ratio techniques adopted in SI engines, improves the part- load performance greatly.

This paper deals mainly with the computer simulation and experimental investigations on a single cylinder, four-stroke, spark ignited, extended expansion engine. The simulation procedure involves thermodynamic and global modeling techniques. Sub-models have been used for predicting heat transfer, friction and gas exchange processes. A two-zone model is adopted for combustion process. Combustion model predicts mass burning rate, ignition delay and combustion duration. It uses sub-models for calculating flame-front area, flamespeed and chemical equilibrium composition of ten product species. Experimentally measured valve-lift data along with suitable coefficient of discharge is used in the analysis of gas exchange process. Unburned hydrocarbons, carbon monoxide and nitric oxide emissions have also been predicted. Experiments have been conducted on a single cylinder, air-cooled, four-stroke, spark-ignition engine.