Disney currently has three types of engines used in our buses.
The most commonly found engine in our RTS bus is the Detroit Diesel 6v92 engine. (183 buses) It's a 6-cylinder turbocharged 2 stroke engine, which means that it's typically harder to keep it a low emission engine. Typically after 100,000 miles, the bus tends to blow smoke as you saw. Buses equipped with a DDEC automatically sense this, and adjust accordingly (in theory) to keep the bus from smoking. Of course, this is at the expense of acceleration. Believe me, Disney is working major overtime to re-tune these engines, and the amount of smokers we have has dramatically decreased. One other thing to note... about 35 of the 6v92's have upper exhausts. While this helps keep the exhaust away from the curbside, it also makes the exhaust a more visible blacker color.
10 of our RTS buses are equipped with the low emission Detroit Diesel Series 50 engine. The S-50 engine is a 4-cylinder turbocharged 4 stroke engine. Because it's 4-stroke, it's quite a bit cleaner burning than the 6v92. However, because they have that top exhaust, they sometimes might emit a small puff of smoke as the turbo spools up. We have recently started to experiment with replacing the 6v92 with a Series 50 engine. Eventually, 10 more buses will be fitted with the S-50. (By the way... despite being a 4-banger... the S-50 has more torque than the 6v92, and can accelerate faster.)
In our 71 Low-Floor buses, we use the Detroit Diesel Series 40 engine. It's a 6-cylinder turbocharged Low Emission engine. These engines are 80% more cleaner burning than the 6v92. Combined with Ultra Low Sulfer diesel fuel, and soot filters, these engines can be just as clean burning as a Compressed Natural Gas engine bus.
One thing to note... each bus has the capability of taking 18 cars off the road every half hour. In a typical day, each bus probably takes off 200-300 cars from the road.
