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Page 84 5 PNGV's Response to the Sixth Report In its previous six reviews, the National Research Council's Standing Committee to Review the Research Program of the PNGV made a number of recommendations, which are documented in published reports (NRC, 1994, 1996, 1997, 1998, 1999, 2000). In the sixth report the committee made specific recommendations related to each of the technologies under development and general recommendations for the program as a whole. Appendix B contains a letter from PNGV to the committee chair documenting PNGV's responses to the major recommendations in the Executive Summary of the sixth report (NRC, 2000). The committee believes that the PNGV has responded well to its recommendations and has been responsive to its suggestions. Discussions of PNGV's responses to the technical suggestions and recommendations in the sixth report are incorporated in the corresponding technical sections in Chapters 2 and 3. Here, the committee simply makes a few points related to the PNGV responses. In recommendation 1 1 the committee suggested that PNGV should quantify and model the trade-off between efficiency and emissions for the power plants under consideration. Recommendation 11 also called for more systems modeling that could quantify the fuel-economy penalty associated with using different technologies to meet the new Tier 2 emission standards, including the effect of vehicle hybridization. PNGV's response was that predictive models do not have the accuracy to perform these trade-off studies or that they are too large, complex, and computationally intensive for use with software, such as Advisor or PSAT, developed for microcomputers. However, the committee has been encour- 1Recommendation numbers correspond to the recommendation numbers in Appendix B.
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Page 85aged by the system modeling studies published recently by MIT and ANL (Weiss et al., 2000; Santini et al., 2001; An et al., 2001). These studies dealt strictly with fuel economies, greenhouse gases, and costs associated with various PNGV technologies, and not Tier 2 emission standards. Nevertheless, the committee believes that, with these studies as examples, the regulated emissions also can be dealt with in a useful, if rudimentary, manner. Even rudimentary modeling with engine steady-state emission maps and estimates of transient emissions (including cold starts and accelerations) would help to answer the question of whether hybridization controls can be adjusted away from the optimum fuel economy and toward reduced emissions. Recommendation 8 called for a major study to determine how well lightweight PNGV vehicles would fare in collisions with the heavier vehicles that constitute the majority of the vehicle population entering service since 1995. As a partial response to safety issues, the Safety Working Group has been formed to identify and prioritize safety issues for PNGV-type vehicles. The committee believes that the formation of the Safety Working Group is a large step in the right direction. The Safety Working Group also recognized the high priority of the weight versus safety issue and has initiated statistical studies using existing accident databases to identify facts and trends pertaining to how vehicle size affects safety. However, the absence of PNGV-type vehicles in the database limits the ability to predict the safety of lightweight vehicles that are not small in size as well. The committee notes that no progress has been made on the fleet modeling study intended to complement the statistical analysis. In view of the difficulty of funding a study of the proposed magnitude, it is suggested that creativity be exercised by the Safety Working Group in defining and initiating affordable studies that would provide the most critically needed information that is lacking from the statistical study. The issue of having an appropriate fuel for advanced PNGV vehicles has been a continuing issue that the committee has commented on in previous reviews. The committee recommended that the PNGV strengthen and expand its cooperative efforts with the petroleum industry. PNGV is exploring the possibility of having a joint symposium with the petroleum industry. It appears that relatively little progress has been made in response to this recommendation, but the committee understands that the petroleum and fuels industry is complex and that developing a good working relationship will take time and much effort on the part of the PNGV and the petroleum industry.
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