The scavenging process of two-stroke engines is unfavourably characterised by the loss of large part of the fresh charge from the exhaust port. Besides, bad combustion and misfire occur at light loads, because of the excessive ratio of residual gas to fresh gas within the cylinder. To avoid fuel short-circuiting to the exhaust port, the solution is direct fuel injection, as well as charge stratification or ATAC are the solutions for light-load operation. With direct fuel injection and charge stratification or ATAC, the simple two-stroke engine with loop-and-crankcase scavenging for motorbikes, thanks to its intrinsic internal EGR, might satisfy the ECE 2002 exhaust emission limits even without catalytic converter. Evolved two-stroke engines should be considered for application on automobiles, since direct injection and charge stratification equalise four-stroke and two-stroke-engines as regards exhaust emissions. Besides, two-stroke engines deliver higher torque, especially at low engine speeds and, of course, have double firing frequency that allows reducing the number of cylinders. In this case, two-stroke engines with poppet valves and external scavenging blower are preferable, to facilitate lubrication and to reduce oil consumption, engine wear and cylinder thermal deformation.
What is the Future of Two-Stroke S.I. Engine?
GENTILI, ROBERTO;Frigo Stefano
1999-01-01
Abstract
The scavenging process of two-stroke engines is unfavourably characterised by the loss of large part of the fresh charge from the exhaust port. Besides, bad combustion and misfire occur at light loads, because of the excessive ratio of residual gas to fresh gas within the cylinder. To avoid fuel short-circuiting to the exhaust port, the solution is direct fuel injection, as well as charge stratification or ATAC are the solutions for light-load operation. With direct fuel injection and charge stratification or ATAC, the simple two-stroke engine with loop-and-crankcase scavenging for motorbikes, thanks to its intrinsic internal EGR, might satisfy the ECE 2002 exhaust emission limits even without catalytic converter. Evolved two-stroke engines should be considered for application on automobiles, since direct injection and charge stratification equalise four-stroke and two-stroke-engines as regards exhaust emissions. Besides, two-stroke engines deliver higher torque, especially at low engine speeds and, of course, have double firing frequency that allows reducing the number of cylinders. In this case, two-stroke engines with poppet valves and external scavenging blower are preferable, to facilitate lubrication and to reduce oil consumption, engine wear and cylinder thermal deformation.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
