The effects of research octane number and fuel systems on the performance and emissions of a spark ignition engine: A study on Saudi Arabian RON91 and RON95 with port injection and direct injection systems Saud Bin Juwair, Taib Iskandar Mohamad, Ahmed Almaleki, Abdullah Alkudsi, Ibrahim Alshunaifi Water and Energy Research Institute, King Abdulaziz City of Science and Technology, P.O. Box 6086, Riyadh 11442, Saudi Arabia
Motivations The internal combustion engine, powering 90% of world vehicles, is the main driver in the transportation sector from which 20% of total world energy is consumed. The engine performance, thermal efficiency and pollutant emissions have a significant impact extending to the environment. Local and global environmental concerns include increased emitted concentrations of carbon dioxide (CO 2 ), carbon monoxide (CO), hydrocarbons (HC), and nitrogen oxides (NOX) that are threats to air quality and contribute to climatic warming. Emissions from the transportation sector are considered a cause of Green House Gases (GHG s) and account for more than 30% of global CO 2 emissions while consuming 63% of petroleum products.
Our research aims to : Experimentally analyze the performance and emissions of a single cylinder, four-stroke spark ignition (SI) engine : Fuelled by two grades of gasoline used in Saudi Arabia, Research Octane Numbers (RON91 and RON95). Operated by two fuel delivery systems; port injection (PI) and direct injection (DI).
Experimental setup
Experimental setup Lotus Single Cylinder Research Engine (SCRE) Lotus SCRE cylinder head Schematic diagram of experimental setup
Test procedures
Test procedures A series of experiments were carried out using two gasoline fuels under varying engine speed from 1500 to 3500 rpm with 500 rpm increment at two engine loads 2.7 bar and 3.7 bar and for two fuel injection systems DI and PI. In the PI system, fuel is injected at 2.3 bar and the start of injection timing (SOI) was at 360 BTDC. While in the DI system, the injection pressure was 100 bar and SOI was at 340 BTDC. Injection timing was controlled to maintain a stoichiometric mixture, and in both systems homogeneous mixture was formed Engine out data were recorded with maximum brake torque (MBT), that were achieved with ignition timings between 16 and 27 BTDC. The engine speed and load were set and measured. Brake power, BSFC, brake thermal efficiency were computed. Emission parameters of CO, THC, NOX and the exhaust gas temperature were recorded using the Horiba gas analyzer. Prior to operating the engine with the tested fuels, the engine was operated using the new fuel for sufficient time to ensure the previous fuel was removed from the fuel system. The in-cylinder pressure was recorded for 100 cycles at a crank angle resolution 0.5.
Results Engine performance Engine exhaust emissions
Engine performance
Variation of brake power against engine speed for RON91 and RON95 at two loads for PI and DI systems
Variation of thermal efficiency with engine speed for RON91 and RON95 at two loads for PI and DI systems
Variation of BSFC against engine speed for RON91 and RON95 at two loads for PI and DI systems
Combustion duration (10-90% MBF)
Engine exhaust emissions
Variation of NOx emissions with engine speed for RON91 and RON95 at 2.7bar load with PI and DI systems Variation of NOx emissions with engine speed for RON91 and RON95 at 3.7bar load with PI and DI systems
Variation of THC emissions with engine speed for RON91 and RON95 at 3.7 bar load with PI and DI systems
The concentrations of CO emissions with engine speed for RON91 and RON95 at 3.7 bar load with PI and DI systems
The findings can be summarized as below : 1. RON91 produces more brake power than RON95 across all speeds and loads regardless of fuel systems which is mainly due to higher heating value. 2. More brake power was achieved by a PI system compared to DI system as charged formation is assumed more homogeneous. 3. Brake thermal efficiency was found higher with RON91 and PI system. 4. The difference in brake specific fuel consumption was small at low speeds and loads, but significant at higher speed and load conditions. Specific fuel consumption with RON95 is lower and in term of the fuel system, the PI system resulted in lower BSFC. 5. Combustion analysis showed a mixed response to different RON and fuel system. Generally, combustion of RON95 is faster than RON91 in both PI and DI systems. DI system with RON95 showed longer combustion duration at low speed and load. The trend is reverse with the RON91 DI system. 6. Combustion phasing happened between 4 and 21o ATDC with majority occurrences around 12o ATDC. 7. NOx emissions of RON91 are higher than gasoline RON95 in most cases except with DI system at high engine speeds. 8. CO emissions of RON91 are higher than RON95 in both fuel systems mainly at higher loads. 9. PI system has an advantage on the THC emissions at low speed but DI system at high speeds produced less THC emissions. THC emission with RON91 is generally higher. 10. Based on all results, utilizing RON91 with PI system is advantageous due to a higher power, better thermal efficiency, and the unit price is 28% lower than RON95. However, using RON95 showed lower BSFC and less NOx and CO emissions were realized.
Future work
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