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Engine systems
Published in Tom Denton, Advanced Automotive Fault Diagnosis, 2020
In modern closed systems, the much lower pressure within the inlet manifold is used to extract crankcase gases. This has to be controlled in most cases by a variable regulator valve or pressure conscious valve (PCV). The valve is fitted between the breather outlet and the inlet manifold. It consists of a spring-loaded plunger, which opens as the inlet manifold pressure reduces. When the engine is stationary, the valve is closed. Under normal running conditions, the valve opens to allow crankcase gases to enter the inlet manifold with minimum restriction. At low manifold pressures during idling and overrun (pressure is less than atmospheric), further travel of the valve plunger against its spring closes it in the opposite direction. This reduces gas flow to the inlet manifold. This feature makes sure that the fuel control process is not interfered with under these conditions. The valve also acts as a safety device in case of a backfire. Any high pressure created in the inlet manifold will close the valve completely. This will isolate the crankcase and prevent the risk of explosion.
Hydrogen
Published in Arumugam S. Ramadhas, Alternative Fuels for Transportation, 2016
Fernando Ortenzi, Giovanni Pede, Arumugam Sakunthalai Ramadhas
In hydrogen engines, premature ignition is a problem because of its lower ignition energy, wider flammability range, and shorter quenching distance. Premature ignition occurs when the fuel mixture in the combustion chamber ignited before ignition by the spark plug and results in an inefficient rough running engine. If the premature ignition occurs near the fuel intake valve the resultant flame travels back into the induction system thus causing backfire. Crankcase oil enters into the combustion chamber through blow-by and in suspended form, or in the crevices just above the top piston ring, and acts as a hot spot that may contribute to preignition (White, Steeper, and Lutz 2006). Preignition in hydrogen vehicles, can be avoided by Injecting cold exhaust gases into the cylinderInjecting cold gaseous hydrogenInjecting water into the cylinderIncreasing the compression ratioUsing lean burn carburetor
Effects of nitrogen film cooling on ignition transition of gaseous oxygen/kerosene spray combustor
Published in Combustion Science and Technology, 2023
Wooseok Song, Dongsoo Shin, Min Son, Jaye Koo
A propellant feed and data acquisition system was developed for the hot firing test, as shown in Figure 3. For the liquid fuel injection, high-pressure gaseous nitrogen was used to pressurize the fuel in the tank. The gaseous oxygen was injected directly from the oxidizer tank with an orifice to control the flow rate. The gaseous nitrogen for the film cooling was sprayed between the outer body of the injector and the combustor with a gap of 0.75 mm, as shown in Figure 2. To prevent flame backfire from the combustion chamber to the propellant lines, check valves were employed. In addition, pneumatic valves along with solenoid valves are used to control the propellant injection. The ignition sequence was controlled using a custom-made microcontroller. Figure 4 shows the ignition sequence for this experiment. To reduce the difference between the sequence signal and actual injection timing, a high-speed camera, manufactured by Photron FASTCAM SA1.1, was used to capture the exact timing. The propellant sequence was set to spray simultaneously. The overall runtime of the hot fire test was 1.5 s, which was sufficient to observe the data from the ignition transition to the steady state of the flame. To measure the flow rate, volumetric flow rates were measured using a turbine flow meter. The mass flow rates of the propellant were calculated from the volumetric flow rate and density, which in turn were estimated from the temperature and static pressure. A type of differential pressure flow meter was used to measure the flow rate of the nitrogen gas. The mass flow rate was constantly controlled via the orifice. National Instruments compact DAQTM data acquisition system was used to monitor and obtain the physical properties; the sampling rate was 10 kHz.
Consequences of ignition timing on a hydrogen-fueled engine at various equivalence ratio
Published in Energy Sources, Part A: Recovery, Utilization, and Environmental Effects, 2022
Jayashish Kumar Pandey, Kumar Gottigere Narayanappa
Like reducing equivalence ratio, a retarded ignition timing (IT) reduces the chances of backfire by reducing the extent of overheating lubricating oil and spark plug. Dhyani and Subramanian pointed out the reduction of knock probability and reported backfire and knock to be interrelated (Dhyani and Subramanian 2018). IT is key to decide an SI engine’s engine performance and combustion and emission characteristics. An early IT increases the cylinder pressure during the compression stroke, resulting in negative compression work (Sayin 2012). While a much-delayed ignition compels the rapid combustion zone away from the top dead center (TDC), reducing the peak pressure and work output (Binjuwair and Alkudsi 2016). Therefore, the COV is also majorly dependent on IT, as a much-retarded ignition leads to chances of abnormal combustion and an early ignition (Su et al. 2017). A retarded ignition compared to other fuels at the same CR is preferred in a hydrogen-fueled engine due to its high laminar burning speed and auto-ignition temperature (Gao et al. 2021a). However, the pressure and temperature increase with increasing CR at the same crank angle, where adequate IT depends on equivalence ratio (Yousufuddin and Masood 2009) since the laminar flame speed is a function of the equivalence ratio. A retarded ignition is responsible for reducing the ignition delay due to relatively high thermal conditions at the time of ignition. However, the total combustion duration may increase due to the falling of the rapid combustion zone in the expansion stroke, increasing the CA10-9032. CA10-90 falls majorly in expansion stroke at delayed ignition; fuel mass burnt cannot overcome the rapid pressure drop caused by the continuous expansion of working fluid (Jeeragal and Subramanian 2019). Therefore, the late combustion period elongates, so the exhaust gas temperature increases. Apart from performance and combustion, ignition time significantly impacts NOx emissions. A major cause of NOx formation is high peak cylinder temperature, which can also be traced with cylinder pressure. However, a delayed ignition reduces the peak temperature, leading to a significant reduction in NOx emissions. Changming Gong et al. reported that CoV increased nearly three times while NOx was reduced to near 0 by retarding ignition by 26°CA (Gong et al. 2019). Under the influence of lean conditions, the effect of retarding ignition is even more profound due to the low flame temperature (Gürbüz and Ih 2021).