Design and Simulation of Two Stroke Engines

INLET FOR r
AIR AND FUEL
Chapter 7 - Reduction of Fuel Consumption and Exhaust Emissions
REED VALVE ? c
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EXHAUST
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INLET
(AIR ONLY)
F/g. 7.JS Alternative stratified charging system of the double piston genre.
operating principle is given in Fig. 7.39, and a photograph of their engine is shown in Plate
7.1. The engine in the photograph is a multi-cylinder unit and, in a small light car operating on
the EEC fuel consumption cycle at 90 and 120 km/h, had an average fuel consumption of 30.8
km/liter (86.8 miles/Imperial gallon or 73.2 miles/US gallon).
The crankcase of the engine fills a storage tank with compressed air through a reed valve.
This stored air is blown into the cylinder through a poppet valve in the cylinder head. At an
appropriate point in the cycle, a low-pressure fuel injector sprays gasoline onto the back of
the poppet valve and the fuel has some residence time in that vicinity for evaporation before
the poppet valve is opened. The quality of the air-fuel spray past the poppet valve is further
enhanced by a venturi surrounding the valve seat. It is claimed that any remaining fuel droplets
have sufficient time to evaporate and mix with the trapped charge before the onset of a
homogeneous combustion process.
The performance characteristics for the single-cylinder test engine are of considerable
significance, and are presented here as Figs. 7.40-7.43 for fuel consumption, hydrocarbons,
and nitrogen oxides. The test engine is of 250 cm 3 swept volume and produces a peak power
of 11 kW at 4500 rpm, which realizes a bmep of 5.9 bar. Thus, the engine has a reasonably
high specific power output for automotive application, i.e., 44 kW/liter. In Fig. 7.40, the best
bsfc contour is at 260 g/kWh, which is an excellent result and superior to most four-stroke
cycle engines. More important, the bsfc value at 1.5 bar bmep at 1500 rpm, a light load and
speed point, is at 400 g/kWh and this too is a significantly low value.
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