This article is a report on a simulation based on Computational Fluid Dynamics (CFD) and an empirical investigation of in-cylinder flow characteristics, In addition, it assesses the performance and emission levels of a commercial-spark ignited engine running on a CNG and Hydrogen blend in different ratios. The main objective was to determine the optimum hydrogen ratio that would yield the best brake torque and release the least polluting gases. The in-cylinder flow velocity and turbulence aspects were investigated during the intake stroke in order to analyze the intake flow behavior. To reach this goal, a 3D CFD code was adopted. For various engine speeds were investigated for gasoline, CNG and hydrogen and CNG blend (HCNG) fueled engines via external mixtures. The variation of brake torque (BT), NO X and CO emissions. A series of tests were conducted on the engine within the speed range of 1000 to 5000 rpm. For this purpose, a commercial Hyundai Sonata S.I engine was modified to operate with a blend of CNG and Hydrogen in different ratios. The experiments attempted to determine the optimum allowable hydrogen ratio with CNG for normal engine operation. The engine performance and the emission levels were also analyzed. At the engine speed of 4200 rpm, the results revealed that beyond a ratio of 50% of the volume of hydrogen added to CNG a backfire phenomenon appeared. Below this ratio (0~40%) of the hydrogen volume, the CNG and Hydrogen blend seemed to be beneficial for the engine performance and for curtailing the emission level. However, at low engine speeds, the NO X concentration increased simultaneously with hydrogen content. In contrast, at high engine speeds, the NO X concentration decreased to its lowest level compared to that reached with gasoline as a running fuel. The concentration levels of HC, CO 2 , and CO decreased with the increase of hydrogen percentage.

This paper studied the effect of variable intake length manifold on filling and volumetric efficiency at starting engine speeds using numerical and experimental process. The investigation is based on acoustic supercharging phenomenon. For this purpose, 1-D engine gas-flow model was developed and optimum intake lengths for several low engine speeds were determined using acoustic theory based-resolution. Using the method of characteristics, pressure waves were predicted at the end of intake line length (intake valve level) in order to test the dynamic inertial supercharging phenomena. The quarter-wave resonator technique was taken into consideration to explore the inlet pressure pulsations. Simulations of pressure wave propagation were achieved during intake stroke and intake valve closed phase. Simulation predictions confirmed the analytically calculated optimum intake length. Numerical investigations were carried out on five in-cylinder flow moving through intake system; air, air-gasoline, air-LPG, air-H2 and air-LPG-H2 blend. The percentages of supplied hydrogen with LPG were 0%, 5%, 10%, 15% and 20% in volume. To experimentally validate the analytical founded lengths, an instrumented cold-flow four cylinder Ford SI engine test bench was prepared. Flow through variable intake length manifold was analyzed. Geometry variation was performed on the plenum length. Three engine low speeds are tested; 500 rpm, 750 rpm and 1000 rpm. The experiment results showed an in-cylinder velocity increase by about 60%, 58% and 48% using the optimal intake length at 500 rpm, 750 rpm and 1000 rpm respectively. Furthermore, the collected data proves that varying intake pipe length continuously with the engine speed leads to an average of 39.7% improvement in volumetric efficiency from the original engine configuration at 1000 rpm.