Low reactivity, compression-ignition, opposed-piston engine
A compression-ignition, opposed-piston engine using a low reactivity fuel as an ignition medium manages trapped temperature and trapped combustion residue within, and fuel injection into, the combustion chambers of the engine, and controls the compression ratio of the engine in order to realize reductions in emissions as well as improved fuel consumption efficiencies.
1. A two-stroke cycle, compression-ignition, opposed-piston engine including at least one cylinder ( 50 ) with longitudinally-separated exhaust ( 54 ) and intake ( 56 ) ports, a pair of pistons ( 60 , 62 ) disposed in opposition to one another in a bore ( 52 ) of the cylinder and a fuel injection system for injecting fuel into a combustion chamber formed in the bore between the end surfaces of the pistons during a compression stroke of the engine, characterized in that:
the combustion chamber has a shape that operatively interacts with swirl and squish flows of charge air to generate one or more tumble flows of air in the combustion chamber;
the fuel injection system includes at least two fuel injectors ( 68 , 70 ) mounted to the cylinder for injecting fuel into the combustion chamber;
the fuel injection system includes a first rail accumulator for delivering a low reactivity fuel to a first fuel injector of the at least two fuel injectors and a second rail accumulator for delivering a high reactivity fuel to a second fuel injector of the at least two fuel injectors; and
the engine includes an engine control unit capable of varying the reactivity of fuel by causing injection of predetermined charges of the low reactivity fuel and the high reactivity fuel in response to engine conditions.
2. A method of operating the two-stroke cycle, compression-ignition, opposed-piston engine of claim 1 , by:
admitting charge air into the bore through the intake port as the pistons move from respective bottom center positions in the bore;
swirling the charge air as it is admitted into the bore;
forming said combustion chamber ( 202 ) between end surfaces ( 61 , 63 ) of the pistons as the pistons approach top center locations in the bore; and,
injecting one or more spray patterns ( 208 , 209 ) of low reactivity fuel into the combustion chamber.
3. The method of claim 2 , in which the low reactivity fuel is gasoline.
4. The method of claim 2 , in which the step of injecting one or more spray patterns includes injecting opposing spray patterns ( 208 , 209 ) of low reactivity fuel in opposing directions along an injection axis ( 203 ) of the combustion chamber.
5. The method of claim 4 , in which the low reactivity fuel is gasoline.
6. The method of claim 2 , in which the step of injecting one or more spray patterns includes injecting first and second spray patterns ( 208 , 209 ) of fuel in opposing directions along an injection axis ( 203 ) of the combustion chamber, in which the first spray pattern includes the low reactivity fuel and the second spray pattern includes a high reactivity fuel.
7. The method of claim 6 , in which the low reactivity fuel is gasoline and the high reactivity fuel is diesel.
8. The method of any one of claims 2 - 7 , further including generating tumble in swirling charge air in the combustion chamber.
9. The method of any one of claims 2 - 7 , in which the engine further includes a variable compression ratio mechanism ( 225 ), the method further including varying the compression ratio of the engine in response to engine speed.
10. The method of claim 9 , in which the compression ratio of the engine is varied by varying phasing between crankshafts of the engine.