Although two-stroke engines have simple mechanical operation and nearly
twice the power per displacement as four-stoke engines, they are losing grasp
of the recreational snowmobile market.
The two-stroke engine has excessive exhaust emissions, noise emissions,
poor fuel economy, and poor low load operation.
If the two-stroke engine is not cleaned up it will be banned from
operation; they are already on their way to being banned from national
parks. This is because of the greater
restrictions being proposed by the National Parks Service (NPS). The NPS is requiring that recreational
The very thing that makes two-stroke engines mechanically simple causes them have poor fuel economy and high exhaust emissions. Unlike a four-stroke that has four distinct cycles- intake, compression, power and exhaust- the two-stroke engine does all of these operations in just two cycles. For an insight into this operation, visit Howthingswork.com
are two very undesirable side effects of the two-stroke cycle, the mixing of
the fresh air/fuel mixture with exhaust gas residuals and the short-circuiting
of the fresh charge. Tests performed at
The largest amount of short-circuited fuel occurs at light-load, low engine rpm operation (Ramakrishnan, 2001). This is due to bad combustion and/or misfire at light load (Gentili, et al, 2001). The poor combustion and misfire is attributed to air-intake throttling. The restriction on the intake side of the scavenging reduces the scavenging ratio and leaves excessive residual exhaust gasses in the cylinder. The large amounts of exhaust gasses present in the combustion chamber lead to misfire and high emissions.