|Drawing of the hybrid locomotive. Click to enlarge.|
GE publicly unveiled a prototype hybrid road locomotive at its Ecomagination event in Los Angeles last week. (Earlier post.) The 4,000 hp locomotive uses a set sodium nickel chloride (Na-NiCl2) batteries to capture and store energy dissipated during dynamic braking as well as an on-board fuel optimizer system.
GE’s work on the hybrid road locomotive is one of the Department of Energy’s Heavy Vehicle Systems Optimization projects, and is one component of GE's larger heavy-duty hybrid efforts that also include buses and very heavy-duty off-highway vehicles such as mine trucks.
The energy stored in the locomotive batteries will reduce fuel consumption and emissions by as much as 10% compared to most of the freight locomotives in use today. Railroads account for about 2.5% of national fuel usage. In addition to reduced emissions, a hybrid will operate more efficiently in higher altitudes and up steep inclines.
Locomotives are electric drive vehicles—the diesel engines function as gensets to power the electric traction motors. Locos use dynamic braking—traction motors ceasing to act as motors and becoming alternators—to decelerate or to maintain speed on a downhill grade. Typically, a resistor is used to dissipate the electric power (about 7,000 hp per locomotive) as heat produced by the electric motor during dynamic braking.
In the hybrid, the energy storage system (ESS) is connected to the main DC link through an electronic converter controlled by an energy management system and associated vehicle system controls. The ESS provides supplemental power to the traction motor along with the power from the genset, and receives power during regenerative braking.
With proper system controls, the hybrid propulsion assist enables reduced output form the diesel, thus reducing the overall amount of fuel required. provide vehicle acceleration with a reduced output power from the diesel engine, thus reducing the amount of fuel required.
Road locomotives’ requirements are significantly more demanding those of automobiles. Locos experience high utilization (an average 8,328 hours per year—a 365-day year has 8,760 hours) over a very wide variety of temperatures. Train coupling delivers significant physical shock, and the steel wheels, steel rails and track irregularities contribute to fairly constant vibration. Locomotives are designed for a 20-year life, and cover about 250,000 miles per year.
Loads range from 1,000 to 4,000 tons per loco, and acceleration and deceleration are of long duration, ranging from tens of minutes to hours.
The hybrid battery system for a locomotive thus needs to provide both high energy and high power. GE’s hybrid prototype has a power/energy (P/E) ratio of about 2. By contrast, the Camry hybrid has a P/E ratio of 19, the GE/Orion V prototype hybrid transit bus a P/E ratio of about 5, and the Sprinter plug-in hybrid prototype with SAFT Li-ion batteries a P/E ratio of about 7, according to GE.
GE considered two variants of NiMH, one li-ion system and two Na-NiCl2 designs before deciding on the Na-NiCl2 pack. Only the sodium nickel chloride batteries passed all the requirements for the system given the application demands, which included: relative weight, relative volume, cooling medium, battery management, cooling impact on size and weight and reliability.
The battery modules are environmentally sealed, thermally insulated and air-cooled, and operate at 300°C. There is module-level monitoring.
The fuel optimization system—which functions with a conventional locomotive as well—factors in trip objectives, speed restrictions, the manifest and track geometry to calculate optimal speed and power settings. This integrates with the hybrid energy management system and the Consist Manager to produce optimized throttle and brake commands and energy flow control to deliver the best efficiency from the entire locomotive “consist”, or package of locomotives (lead and trailers) that move the train.
Even without the hybrid propulsion system, GE’s Consist Manager can improve fuel economy between 1% and 3% for each locomotive.
Before the GE hybrid locomotive is offered commercially, the engineering team will continue work and analysis on the batteries and corresponding control systems on-board the locomotive. Following lab testing, GE will produce pre-production units for customer field validation purposes.