THE JOURNAL OF ENGINE RESEARCH
Year:2015 | Volume:11 | Issue:39|Papers Count:6

Operating an engine with homogeneous charge compression ignition (HCCI) technique is a promising technique to lower NOx and PM emissions of engines while achieving high efficiency and lower fuel consumption. Nevertheless, applications for HCCI are still limited due to the absence of a definite means to control ignition timing and narrow operating region. A single cylinder diesel engine with compression ratio of 19.3 has been used for running in HCCI mode. The operating region in this study was defined based on l and EGR. For fixed values of compression ratio, intake temperature and engine speed, demand for a particular engine output can be met by varying combinations of l and EGR. All experimental tests have been done in intake temperature of 75oC, exhaust pressure of 137 kPa and engine speed of 1600 rpm. Amount of EGR varied from 0 to 41 percent in tests. The results indicated that EGR can expand the HCCI operating regions into part loads (imep = 5.4 bar). At any constant EGR line, HC and CO increased by increasing l. general trend of lower HC and CO emissions at higher EGR rates is just because of the mixture quality that is near to stoichiometric at higher EGR fractions. EGR itself increased HC and CO emissions as it was expected.

Nowadays, utilization of blended fuel in internal combustion engine is one of main topics in vehicle industries. The synergy effect will be highlighted when the potential of each fuel is employed and the engine performance will improve consequently. In this research, the laminar flame speed of methane (main component of reference fuel for Natural gas) and isooctane (main component of reference fuel for gasoline) and their blended fuel, as an intrinsic characteristic of combustible mixtures is measured. Isooctane and methane with two volumetric fractions of 70% and 95% in blended are added in constant volume combustion chamber with partial pressure method in three temperature of 368, 408 and 448K and three pressure of 1, 2.5 and 5 bar. After filling the chamber in specified fuel air ratio, the mixture is ignited at the center of chamber and flame propagation is recorded with schlieren method. Laminar flame speed and Markstein length are calculated via post processing of flame images. Numerical simulation of flame speed is done using CHEMKIN code. Finally, a correlation based on temperature, pressure, equivalence ratio and methane mass fraction in blended fuel is proposed which predict the flame speed well.

Main purpose of current study is development of a new multi zone model for direct injection diesel engines. Zone configuration is based on conical shape of spray. Siebers’s correlation is used for spray cone angle calculation. Experimental data are used for calculation of fuel inlet mass flow rate. Fuel diffusion in different zones is calculated using Fick’s law. A chemical kinetics mechanism consisting of 76 species and 327 reactions is used for simulation of combustion chemistry. The chemical kinetics mechanism contains 6 reactions for soot formation simulation and 14 reactions for NOx formation simulation. Results are in good agreement with experimental data in wide range of engine operating conditions. Maximum error of model in soot prediction is 20% and in NOx prediction is 15%.

Marine diesel engines are in the heavy duty diesel engines group with high output power. These engines have wet liner sleeve that cooling water surrounded it. The cooling heat transferred to space water. The engine combustion in one side and cooling water and liner interaction at other side create different physical and chemical phenomena. Liner cracking and fracture is probable phenomenon and have different reasons such as over thermal stresses, cavitation or corrosion. These failures cause to general engine overhaul and liner replacing. This paper presents the study of liner cracking of V12 marine diesel engine. The results have shown that the increasing of the cooling water temperature accelerates the liner fatigue and cracking. Liner corrosion and cavitation have additional effects on this failure.

One of the most important matters that have a great effect on engine efficiency is engine internal friction. In this article the friction model of piston-cylinder mechanism has been numerically simulated for a 4 cylinders spark ignition engine. The results were validated and the test results have been compared with simulation results. Consequently, the effect of combustion pressure and temperature, on the friction of ring and piston has been studied. Also, the impact of piston clearance on engine friction has been numerically investigated. The simulation results showed that at speeds of less than 3000 rpm varying the piston-liner clearance cannot significantly change the engine friction. But increasing clearance from the 30 to 80 microns at 6,000 rpm caused about 20% reduction in friction. It was also seen that the consideration of combustion pressure and temperature leads to a considerable increase in the engine friction.

Since spark ignition engines has a large portion in emission production, recognition of the engine emissions when engine work at high compression ratios and different conditions with gasoline and natural gas could be useful to compare engine exhaust emissions in gasoline and natural gas fuel case and find the lowest emissions production condition. In the current work, an engine was set at 9 and 10 compression ratio for gasoline and natural gas fuel case. It warmed up with fuel injection at full load, three engine speeds, at certain spark advance and four equivalence ratios. Then in each engine speed and equivalence ratio, spark advance (according to the crank angle) was changed on non-knock domain with two degree per step and external results were recorded. External data included HC and CO emissions, relative air-fuel ratio (l), also internal air-flow and external torque. It was observed that the decrease of representative equivalence ratio causes the reduction of HC and CO. At equal representative equivalence ratio the amount of HC in gasoline fuel case is more than natural gas fuel case and overall increasing was estimated more than three times. Engine speed change causes variation in the amount of HC while it has no impact in the amount of CO.