[quote="mtuandrew"]Most two-stroke engines don't (and can't) have fully variable valve timing, which can help control emissions and increase power for a four-stroke, and don't burn their fuel as completely as a four-stroke engine. They're also more difficult to fit with pollution controlling fixtures like exhaust gas recirculation.[/quote]
This statement does not apply to the EMD 2-stroke engine. There is no intake valve on it, and no need for one. The cylinder has ports that become uncovered as the piston is on the bottom end of the stroke, the start of the intake portion of the cycle. These allow combustion air to come into the cylinder and help force out the last of the remaining combustion air. These then are covered as the piston moves up making the compression part of the cycle, fuel is injected into the cylinder as it is at the top, forming the combustion part, the piston moves down and the exhaust valves open to end the power part of the cycle.
The 710 burns all its fuel as well as any 4-stroke engine, very little is left unburned, particulate isn't the real problem with the engine, but NOx is. If unburned fuel was a problem, the engine would never have been in production so long. There are three main items involved in pollution control - CO, NOx, and particulates. The EMD 710 made the Tier 2 emissions without major problems, but it involved new fuel injector design and aftercoolers to keep from losing fuel efficiency. You see, to burn fuel to get the most power would end up with large amounts of nitrogen oxides, NOx, be generated. To reduce NOx requires reduced combustion time so the nitrogen in the air isn't burned.
All modern locomotives have a power meter, that measures the amount of power generated while in service. Over the course of several months, as long as the actual fuel used is carefully recorded, the efficiency of the engine can be determined. The railroads all know that the 710 & GE engines are about the same, not that big of a difference in fuel savings of one over the other. However, the GEs cost less to buy so they have won the sales.
EMD's 265 4-stroke H-engine actually is the most efficient out there, but it is new, had some problems during its inital production runs (new production problems, not design problems that couldn't be fixed) and railroads don't like new things and don't want any production problems, plus the intial cost was still too high. Fuel savings alone couldn't sell the engine, but maybe it will eventually. Personally I think fuel cells burning a hydrogen fuel will be the eventual replacement for diesel engines. EMD built one six years ago using the GM fuel cells, but I think that is lost now that EMD isn't part of GM.
This statement does not apply to the EMD 2-stroke engine. There is no intake valve on it, and no need for one. The cylinder has ports that become uncovered as the piston is on the bottom end of the stroke, the start of the intake portion of the cycle. These allow combustion air to come into the cylinder and help force out the last of the remaining combustion air. These then are covered as the piston moves up making the compression part of the cycle, fuel is injected into the cylinder as it is at the top, forming the combustion part, the piston moves down and the exhaust valves open to end the power part of the cycle.
The 710 burns all its fuel as well as any 4-stroke engine, very little is left unburned, particulate isn't the real problem with the engine, but NOx is. If unburned fuel was a problem, the engine would never have been in production so long. There are three main items involved in pollution control - CO, NOx, and particulates. The EMD 710 made the Tier 2 emissions without major problems, but it involved new fuel injector design and aftercoolers to keep from losing fuel efficiency. You see, to burn fuel to get the most power would end up with large amounts of nitrogen oxides, NOx, be generated. To reduce NOx requires reduced combustion time so the nitrogen in the air isn't burned.
All modern locomotives have a power meter, that measures the amount of power generated while in service. Over the course of several months, as long as the actual fuel used is carefully recorded, the efficiency of the engine can be determined. The railroads all know that the 710 & GE engines are about the same, not that big of a difference in fuel savings of one over the other. However, the GEs cost less to buy so they have won the sales.
EMD's 265 4-stroke H-engine actually is the most efficient out there, but it is new, had some problems during its inital production runs (new production problems, not design problems that couldn't be fixed) and railroads don't like new things and don't want any production problems, plus the intial cost was still too high. Fuel savings alone couldn't sell the engine, but maybe it will eventually. Personally I think fuel cells burning a hydrogen fuel will be the eventual replacement for diesel engines. EMD built one six years ago using the GM fuel cells, but I think that is lost now that EMD isn't part of GM.
