Combustion Characteristics Of Homogeneous Charge Compression Ignition Engine Research Articles

Predictive simulation of single cylinder n-butanol HCCI engine

Homogeneous Charge Compression Ignition (HCCI) is a commonly research new combustion mode due to its advantages over conventional combustion in internal combustion engine such as higher thermal efficiency as well as lower particulate matter (PM) and nitrogen oxides (NOx) emission. However, combustion phasing control difficulty is the main challenge in order to achieve this HCCI combustion due to the absence of direct auto-ignition control. The aim of this study is to investigate the effects of engine load conditions, intake charge temperature and exhaust gas recirculation (EGR) rate numerically on the combustion characteristics of HCCI engine in a single-cylinder and four-stroke engine fuelled with n-butanol. Predictive one-dimensional engine cycle simulation with single-zone model is employed in this study. A chemical kinetic mechanism of n-butanol is used to in this model to capture the chemical reaction process during the combustion. It was found that these parameters play important roles towards the combustion phasing of the HCCI engine as well as the in-cylinder pressure. This HCCI model is able to predict the trend of the combustion characteristics comprehensively with the variation of these critical parameters resulting in a good agreement with previous HCCI studies.

Optimized ANN-GA and experimental analysis of the performance and combustion characteristics of HCCI engine

HCCI (Homogeneous Charge Compression Ignition) engine has the benefit of operating at high thermal efficiency and low emissions of NOx and soot. However, it has challenges of complex combustion phase controlling and low operating range. This research work investigated the performance and combustion characteristics of HCCI engine with numerical simulations on ANSYS FLUENT and neural network models. The numerical and neural network results were validated by experimental observations with different fuel properties and reduced valve lifts for trapping of the exhaust gases. Experiments were performed on a SMART engine for different speeds and inlet air temperature, with various reference fuels (PRF30, PRF50, PRF70) and methanol to validate the CFD and ANN-GA observations. The engine performance was analyzed for IMEP, ISFC and thermal efficiency, which were found to be 8.2 bar, 205 g/kWh and 44.5% respectively as the optimum performance with PRF-70 fuel. The trapping of the residual gases was performed with various fuel blends in order to overcome the cyclic variations and to improve the operating zones near the knock boundary. The heat release rate was significantly reduced with trapped exhaust gases, and operating region was improved with the use of methanol fuel. Overall the trapping of the hot residual gases resulted in the maximum increase in the operating region by 12% and reduced cyclic variations by 15% for methanol fuel. The exhaust emissions were analyzed and ultra-low emissions of NOx at lean operating conditions were observed with the reduced valve lifts. The study results indicated thermal NO emissions on an average were decreased by 7.8%, CO emissions reduced by 6% and HC emissions increased by 9%. Methanol had ultra-low emissions of HC and CO, but higher emissions of NO and PRF30 had lower emissions of NO. However, ANN-GA model gave satisfactory combustion characteristics and emissions with respect to experimental results. Thus, CFD simulations, Neural Network methods and experimental study gave valuable thoughts of trapped residual gases approach on performance, combustion and emission characteristics of HCCI with PRF’s and methanol fuel.

Effect of Ethanol–Diesel Fuel Blends on Autoignition and Combustion Characteristics in HCCI Engines

The combustion process in homogeneous charge compression ignition (HCCI) is mainly controlled by the chemical kinetics reactions of the fuel-air mixture. So, the HCCI combustion process is sensitive to the charge temperature, pressure, and the mixture composition during the compression stroke. In the present work, the simulations results of the HCCI combustion are performed using a single zone model with detailed kinetic reaction mechanism. The simulation study is achieved to predict the auto-ignition timing and the combustion characteristics of the HCCI engine fueled with blends of ethanol and diesel at different volume percentage. The premixed ratio of the ethanol–diesel fuel blends is used in this study to control the auto-ignition timing and the combustion characteristics at a wide range of the engine load. The main pathway of this work is to study the influence of engine operating parameters which including the premixed ratio, fuel-air equivalence ratio on the combustion characteristics of HCCI engine. These effects are studied and traced through the simulation result data of the in-cylinder pressure, temperature, and heat release at different premixed ratios of ethanol-diesel fuels blends of 0, 10, 20, 30,40 and 50% (by volume). The engine speed is kept constant at 1500 RPM. The obtained results show that the increase of the premixed ratio of ethanol in diesel fuel blends in the range up to 50% will decrease the peak cylinder pressure and temperature and decrease the combustion duration.