The hottest - Ricardo

percent of the entire global market,
with more likely to follow. All the more
remarkable is the fact that the Split
Carburettor concept costs virtually
nothing extra to manufacture since it
essentially comprises a modification
to an existing design, yet is set to save
two-stroke engine manufacturers
world-wide hundreds of millions of
Dollars.
Two-stroke engines have many
advantages over four-strokes in some
applications, including low weight,
simplicity, high power output and
typically 25 per cent lower
manufacturing costs. In fact, as group
head Paul Etheridge explains, when it
comes to hand-held utility products,
conventional four-stroke engines have
definite limitations. “Hand-held
products have to work in any altitude
but if you turn a wet sump lubricated
four-stroke engine upside down, the
oil disappears into the cylinder head.
Response and torque backup are
inferior to the two-stroke, they’re
heavier and they cost more money to
make. In fact there is a huge raft of
issues with the four-stroke.”
Two-strokes: environmentally
poor – until now
Unfortunately, when it comes to
exhaust emissions (in standard form
at least) the unregulated two-stroke
engine is something of an
environmental bandit. Each time it
ingests a fresh charge of fuel, some of
it is expelled with the outgoing
exhaust: this results in a level of
unburned hydrocarbons which makes
a puff of modern car exhaust appear
like a breath of fresh Alpine air. “About
30 per cent of the fuel you put into a
conventional two-stroke engine
passes straight through without even
being burned,” Etheridge continues,
“so you get around 10 times the
hydrocarbon emissions of a fourstroke.”
Catalytic converters have been
tried but proved unsuccessful in many
products because of their not
insignificant cost, bulk and also
because the high temperatures they
generate could injure operators and
cause fires.
Not surprisingly, legislators are
clamping down on these engines. If
manufacturers want to use two-stroke
power beyond 2008-2010 they will be
forced to think again in order to meet
stringent US and European emissions
regulations aimed specifically at handheld
utility engines. The most popular
way of achieving that is to use a new
design of two-stroke known as the airhead
stratified charge engine, which
introduces what is in effect an air wall
immediately in front of each incoming
charge of fuel and air. As a result, any
Q2, 2006 • RICARDO QUARTERLY REVIEW 15