Summary of Analytical Objectives

Based on cumulated background knowledge surrounding plug-in hybrid vehicle development and on-road emissions testing capabilities, finding novel and unique approaches to analyzing the Sprinter PHEV on-road emissions and operating data was a relatively

straightforward process. The Plug-In Hybrid Sprinter Demonstration Study funded by KU’s Transportation Research Institute (TRI) is the first research endeavor focusing on on-road emissions and operation of an original equipment manufactured plug-in hybrid vehicle. Prior to this work, the only data available to the public domain concerning PHEVs was based on hybrid electric vehicles retrofitted with plug-in capabilities. The diesel configuration of the Kansas City PHEV provides an additional dimension of originality to the study. Available research surrounding hybrid electric vehicle (HEV) on-road operation and emissions is largely limited to gasoline configured HEVs. Generally speaking, diesel HEVs are not part of the regular on-road HEV fleet, so information regarding the use of a diesel internal combustion engine in hybrid electric applications is limited at best. Using the inherent novelty of the PHEV Sprinter Demonstration Study a primary focus, five primary data-analysis objectives were identified for further investigation.

4.2.1 Objective 1: Vehicle Specific Power Analysis

As a commonly used proxy for estimating a vehicle’s on-road power demand, vehicle specific power (VSP) analysis often accompanies on-road emissions campaigns.

Additionally, VSP has been found to better predict on-road vehicle emissions than any single drive or road-based parameter (i.e. velocity, acceleration, grade, etc.). Due to its predictive abilities, VSP categorization techniques have become the backbone to current modeling

efforts. Because the PHEV possesses the ability to operate both as an electric-only vehicle and as a conventional hybrid electric vehicle, it presented a degree of uncertainty regarding its suitability and applicability towards current emissions models. Objective 1’s primary focus was to perform a comprehensive vehicle specific power analysis to the on-road PHEV data. This investigation applied VSP classification techniques to the PHEV on-road data as a means of assessing the feasibility of applying current models to the alternative-powered drivetrain.

4.2.2 Objective 2: Roadway Type Analysis (Urban/Suburban /Highway)

Where Objective 1 provides an overall investigation and assessment of the PHEV’s on-road emissions and operation, Objective 2 refined its scope to evaluating the effect that roadway type has on the PHEV’s operation. Frey et al. (2008) found that velocity,

acceleration, and road grade were significant factors when evaluating variations in inter-vehicle emissions. The Sprinter PHEV was specifically designed to excel in urban, stop-and-go traffic by maximizing its electric drive capabilities and, thus, minimizing its total

emissions. The study methodologies were purposely designed in order to showcase the PHEV’s operation according to different road-types: urban, suburban, and highway. As part of this analysis, roadway-type was defined by geographic location as well as by on-road traffic profile. The PHEV Sprinter’s operating characteristics (power scheme and demand, electrical recuperation, and fuel use) and emissions profiles are investigated according to roadway type.

4.2.3 Objective 3: PHEV Operating Mode Analysis

Efficient use of the internal combustion engine, effective utilization of electric drive capacity, and successful integration of the two systems define PHEV proficiency. The PHEV Sprinter was designed to function under two distinct operating modes:

charge-sustaining and charge-depleting. Charge-depleting mode is defined by the PHEV’s ability to store electrical capacity acquired during grid-based charging periods. The primary objective of charge-depleting operation is to efficiently use the stored battery capacity to provide a significant amount of electric-only operation. Once the battery capacity reaches a moderate state of charge, the PHEV then switches to a more conservative, charge-sustaining power scheme. During charge-sustaining mode, the PHEV functions as a conventional hybrid electric vehicle, by maintaining a nominal battery charge. Electrical recuperation provides electrical drive capacity during charge-sustaining mode, but any excess stored battery potential has already been expired during charge-depleting operation. The Phase I PHEV Sprinter’s were designed to achieve 20miles of electric drive capacity with a full charge.

However, initial observation of the Kansas City PHEV Sprinter led the field engineer to doubt the KC PHEV’s ability to realize 20miles of electric drive during charge-depleting operation. In addition to investigating the PHEV Sprinter’s electric-only range during charge-depleting mode (one of the defining features of PHEV technology), nuances in electric-only and hybrid operation between the two operating modes will be investigated in depth.

4.2.4 Objective 4: Diesel Internal Combustion Engine (dICE) as Utilized in the Plug-In Hybrid Vehicle Context

The proof-of-concept Phase I PHEV Sprinter study was one of the first studies presenting diesel hybrid electric vehicles. There are several operating characteristics

regarding diesel ICE operation that may or may not be best suited to PHEV application. For example, in cold operating temperatures, it is possible that the diesel oxidation catalyst rarely reaches sufficient operating temperature to effectively control carbon monoxide and

hydrocarbon emissions during high state of charge operation (when the diesel engine is only used as needed). Heywood (1988) noted that during transient diesel operation, instances of increased emissions load were likely. The on-demand use of the ICE in the PHEV context could result in an otherwise clean and efficient diesel ICE operating in a mostly transient nature. Sonntag et al. (2008) reported higher particulate matter emissions from diesel hybrid electric buses than conventional diesel buses when the direct oxidation catalyst (DOC) was the only after treatment technology utilized. The 4^th objective focuses on the efficacy of using a diesel ICE in the PHEV application according to the KC PHEV Sprinter’s on-road behaviors. Collins et al. (2007) reported emissions spikes from diesel engines due to both cold starts and transient events encountered during hot running conditions. Because the potential of encountering both cold starts and transient engine events is high with plug-in hybrid operation, a detailed investigation regarding the behavior of the diesel engine in the application is presented.

4.2.5 Objective 5: PHEV On-Road Vocation Analysis

Drive cycle and vehicle vocation (purpose) have been shown to be significant factors effecting on-road emissions and vehicle behaviors (Clark et al. 2002). The bulk of the studies investigating this have been primarily concerned with the ultimate impact on

emissions from a meso- or macro-scale. However, the intricacies behind the differing cycles have not been fully investigated. During preliminary sampling efforts, distinct differences between transit operation (replicated by following or shadowing a transit bus) and normal, civilian driving (solo) were observed. In order to evaluate the differences between transit versus normal on-road operation, the data were investigated on two fronts: on-road

behavioral differences (velocity, acceleration and deceleration profiles, and power output), and the impact on the PHEV Sprinter’s operation (electric-only range during charge-depleting mode, overall hybrid operation within the two operating modes, regenerative breaking, fuel economy, and emissions loads and profiles).

Chapter 5: Temperature/Auxiliary System Analysis