Title : Influence of variable compression ratio on emissions of a single cylinder- 4 stroke engine fueled with/etanol/gasoline blends
Introduction: Changing engine design system and exhaust control management are costly and limited. Researcher's priority is looking for alternative fuel and clean energy resources. Alcohol fuel is the answer to this problem; methanol, ethanol, etc. are the alternative fuel for automobiles using spark ignition engines, as they have several physical and combustion properties (e.g. chemical stability and control corrosiveness) similar to gasoline.[1-4]. This manuscripts presents HC, CO and NOx emissions analyses under different compression ratios.
Experimental: The tests were performed on a four-stroke single-cylinder equipped with air cooling, CT 152 with power 1.2KW and gasoline engine. The engine cylinder bore is 65.1 mm, and a stroke of 44.4 mm, with an original CR of 5:1 to 10:1 also 5 variable compression ratios were available and adjustable by changing engine cylinder head. Ignition timing was adjustable in 11 stages: 10° after TDC to 40° before TDC, Belt pulley: Ø 125 mm; the engine was installed on CT 159 test stand. The engine has a sensor for measuring the exhaust gas temperature. The sensor, ignition cut-off as well as air and fuel supply were connected to the CT 159 test stand. In order to determine the engine torque, force transmission to brake was connected via pulley on the test .Horiba MEXA 7100 DEGR (HC, CO, NOx, and CO2) was connected to measure the exhaust emissions downstream the exhaust.
Results and Discussion: Unburned HC is presented mostly in the C5 condition of unleaded gasoline . Any change in the compression ratio will affect the HC emissions because when increasing compression ratio the combustion chamber becomes larger, so the surface to the volume ratio also increases, in turn, HC emissions gets more, and reach the maximum concentration of 920 ppm and reduces to 820 ppm. As noticed in C1 condition. It is very clear that, the geometry of the combustion chamber plays an essential role in controlling HC emissions. In the presented tests, HC emissions were reduced by two different mechanisms. as the load is increasing; the temperature of the mixture inside the cylinder gets higher which leads to higher combustion temperature and promotes complete oxidation. While more stratification was applied, two affecting factors were presented. Firstly, increased stratification lead to higher fuel concentration in the bulk-gas, which means higher combustion temperatures and complete combustion is achieved. Secondly, increased stratification brings small amounts of fuel in the quenching zones. Moreover, drops in the combustion gas temperature at low load dominate incompletion of the combustion process and cause higher HC. Similarly, reducing engine load leads to an increase in CO emissions. However, all used fuels, with increasing compression ratios CO, and NOx emissions were increased. The lowest NOx emission was obtained from gasoline blends with 20% ethanol, which has the highest heat vaporization rate .
Conclusions: CO, CO2 and NOx emissions are influenced by engine operation and changing compression ratios of the engine. HC and CO emissions were slightly higher in larger CRS while NOx emission is found to be more influenced by changing CRs, CO2 showed an increase when thermal efficiency was improved during the combustion. Using biofuel, gasoline blends has a huge impact on the tailpipe emissions Analysis shows HC, CO, and NOx was dramatically reduced; CO2 was presented more in higher compression ratio.