What are two stroke engines? (Yes, this is about engines)
As always, the wikipedia article briefly explains what two stroke engines are, but that’d hardly help to recognise the last few of these on Indian roads. If you ever felt that odd looking bike on road is making shriller noise ands emits a bit more smoke than the other bikes on road, good chance that those are two strokes, which ruled the Indian roads in another era, the 1970s and the 80s and well into the 90s. In case you recognize the Rajdoots, Yezdis and the Yamaha RX100s and RD350s, Bajaj Chetaks, Lamby, Lambretta, Priya, Vijai Super, LML Vespa, Suzuki Shogun, Samurai, Tamil Nadu’s own TVS 50, Bajaj RE Autos and thus goes the list. There still are a quite a lot of these remaining in Indian roads, driving memories of generations which grew up seeing/riding these vehicles.
Why Two Strokes a few decades back?
While I am not sure of the business reasons why these engines where chosen over four stroke counterparts in those days, following things would definitely have featured in the list when the decision was made.
- Lesser moving parts compared to four strokes, easier and less expensive to manufacture.
- Low on maintenance. (again due to lesser moving parts)
- Higher Power to Weight (Size) Ratio. Not a major decider for 2/3 wheelers, but a definite winner for two stroke engine technology.
Why Two Strokes are getting removed from streets?
- Two strokes do not have valve arrangements, rather have intake and exhaust ports, which are controlled by the reciprocating piston’s movement. While this results in minimum moving parts, it also results in loss of efficiency because a part of the fresh charge (air fuel mixture) entering the combustion chamber will be lost without getting burnt. That’s like, your vehicle doesn’t move as much as the fuel is worth! Pretty big sin given the high price of fossil fuels.
- This inefficient combustion results in low fuel efficiency and increased pollution due to the unburnt air fuel mixture.
- In an era where the fossil fuels are fast getting consumed, inefficient fuel utilisation and pollution are definitely not desired.
The new stringent rules on pollution control and fuel efficiency and market demand for more mileage per litre of fuel pushed out these machines from production and many of the above listed vehicle manufacturers, who could not adapt to the technology change had to shut down shop in India. There still are fans of two stroke bikes, who cherish the quick pick up and the head turning shrill noise that these machines make. Yamaha RX 100s, Bajaj Chetaks can still be commonly found in almost all Indian roads, where as Jawa, Yezdi and RD 350s have become pride posessions and are becoming rarer by the day.
After reading this much, in case you concluded that two stroke technology is a thing of the past, there you got it wrong. Two stroke engines are still very much in use and in the largest of possible sizes propelling behemoths of ships across the world’s oceans. Though not exactly similar in construction compared to the smaller petrol two strokes, large, slow speed, direct coupled, diesel two stroke engines propel majority of the world’s merchant marine fleet, the backbone of all the global resource availability in modern times.