CNG Transit Bus Propulsion
Although the DDC natural gas engine was removed from the transit market, Cummins Westport Inc. and John Deere offer transit bus engine options for natural gas propulsion. Both manufacturers recently announced intentions to have standard-size, transit-bus, natural gas engines that meet the 2010 emissions certification levels available in model year 2006.
Cummins Westport is a joint venture between Cummins Engine Company and Westport Innovations. It has three main natural gas engine platforms:
B Gas Plus (5.9 L)—Horsepower: 195, 200, 230; torque: 420, 465, 500 lb-ft
C Gas Plus (8.3 L)—Horsepower: 250, 275, 280; torque: 660, 750, 850 lb-ft
L Gas Plus (8.9 L)—Horsepower: 320, torque:1000 lb-ft
John Deere has one commercial natural gas engine product (6081H), which has the following settings:
6081H (8.1 L)—Horsepower: 250, 275, 280; torque: 735, 800, 900 lb-ft
Both these natural gas engine manufacturers are working to make a life-cycle cost advantage for natural gas fuel use compared to equivalent diesel fuel use and diesel fuel costs.
BAE Systems HybriDrive Propulsion System
NYCT’s hybrid buses are built by Orion Bus Industries (a part of DaimlerChrysler Commercial Buses North America) and use the BAE Systems HybriDrive propulsion system (Figure 1).
In this series hybrid electric system, a relatively small diesel engine running at an optimal controlled speed is connected to a generator that produces electricity for the electric drive motor and batteries. The electric motor drives the vehicle and acts as a generator to capture energy during regenerative braking. The batteries supply additional power during acceleration and hill climbing and store energy recovered during regenerative braking and idling. The battery optimization subsystem monitors and maintains the charge of each individual battery. The propulsion control subsystem manages the entire system and optimizes performance for emissions, fuel economy, and power.