MNTRC Newsletter Vol 19, Issue 1: Summer 2012

Larson Institute plans its research for MNTRC

Michael Casper, Pennsylvania Transportation Institute

Penn State is investigating thermal management for lithium ion battery packs in several environments and conditions.

Penn State News – The Larson Institute at Penn State is underway with planning for its research under the new Mineta National Transit Research Consortium. Work at the Larson Institute’s Bus Research and Testing Center informs significant progress in policy, technology and environmental issues. Senior researcher Suresh Iyer and the Center’s director, David Klinikowski, attended the May 2012 American Public Transportation Association’s Bus & Paratransit Conference . He is pleased to have been named Vice Chair of Government Affairs and Regulation for the Clean Propulsion Committee. The following research summaries represent project ideas for which funding is currently being sought.

Advanced Bus Specification Research

Currently, the transit bus marketplace offers a large heavy-duty or a cutaway chassis-based bus in a variety of lengths and seating configurations. Larger transit agencies use the large buses for urban route transit and the cutaway buses for paratransit service. However, for smaller non-urban transit agencies, neither of these choices is optimal.

At the same time, smaller agencies cannot afford two different dedicated fleets. Ideally their buses must provide transit service in peak hours and then paratransit service in off-peak hours – and do so reliably and safely. Many smaller agencies operate in rural areas where roads are challenging for most buses to traverse and perform reliably. 

These buses require significant maintenance, or they are replaced early. A new type of bus could satisfy the needs of smaller agencies. But lack of technical specifications precludes manufacturers from building this type of design. Some design experiments have been done, but performance characteristics have not been documented.
The research objective is to identify and quantify technical characteristics for a new transit bus that is accessible, versatile, reliable, durable, and efficient in all operating environments. This research could be leveraged to prepare a request for proposal (RFP) for the new type of bus. The payoff potential is great. Increased durability could significantly reduce life-cycle cost and reduce the number of different vehicles required for adequate service.

Build Out of CNG Diesel Dual Fuel Application Matrix

A previous project investigated the potential of a diesel and CNG dual-fuel system to reduce fuel costs for a late-model heavy truck. Emphasis was placed on substituting diesel with less costly natural gas. An aftermarket dual fuel kit was installed on a 2012 Mack Granite truck. 

In parallel, engine dynamometer testing was performed to determine sensitivity of fuel economy and emissions to various engine control parameters and mixture ratios. A comprehensive economic model predicted good return on investment at reasonable CNG substitution levels and modest fueling infrastructure investment. Findings from engine testing provided a baseline for an onboard electronic “patch box” to control the diesel CNG fuel ratio and mass while maintaining the stock engine power curve and emissions. 

The patch box read available engine data and altered the accelerator pedal signal received by the stock diesel engine. The box’s effectiveness at improving fuel economy while maintaining emission levels was limited by its access to diesel engine data and control parameters and the achieved tuning level.  

This new project will build out the application matrix across a much wider range of heavy truck and transit bus model years, engine technologies, and available engine control signals. Economic analysis will help identify several truck and bus models with the greatest potential return on investment. The technology will be systematically applied to identify models across the fleet in phases consisting of survey, analysis, implementation, and validation.

Thermal Management of Li-ion Battery Energy Storage Systems

Large-format cylindrical and prismatic cell Li-ion battery packs are emerging in the automotive industry. Each cell structure poses unique thermal management challenges. In heavy vehicle and/or high power applications, thermal management is particularly significant regarding battery safety, performance, and life.

The project will include a review of current designs and simulation, analysis, validation and optimization of potential thermal management designs for both large-format cylindrical and prismatic Li-ion cell packs under both normal driving and fast-charge conditions, and in various environments, including temperature and humidity. The research will examine representative power duty cycles of batteries for transit bus operation under selected climate conditions; evaluate different cooling methods such as liquid cooling versus forced A/C air cooling; and ultimately optimize the thermal management system.

The research will also analyze differences between new batteries and batteries that have been used in normal operational conditions for up to three years, noting the differences in thermal management effectiveness, pack performance, and life.