Effect of Air-Conditioning on Light Duty Gasoline Vehicles Fuel Economy

Abstract

With more stringent U.S. fuel economy (FE) standards, the effect of auxiliary devices such as air-conditioning (AC) have received increased attention. AC is the largest auxiliary engine load for light duty gasoline vehicles (LDGVs). However, there are few data regarding the effect of AC operation on FE for LDGVs based on real-world measurements, especially for recent model year vehicles. The Motor Vehicle Emission Simulator (MOVES) is a regulatory model for estimating on-road vehicle energy-use and emissions. MOVES adjusts vehicle energy-use rates for AC effects. However, MOVES-predicted FE with AC has not been evaluated based on empirical measurements. The research objectives are to quantify the LDGVs FE penalty from AC and assess the accuracy of MOVES2014a-predicted FE with AC. The AC effect on real-world fleet-average FE was quantified based on 78 AC-off vehicles versus 55 AC-on vehicles, measured with onboard instruments on defined study routes. MOVES2014a-based FE penalty from AC was evaluated based on real-world estimates and chassis dynamometer-based FE test results used for FE ratings. The real-world FE penalty ranges between 1.3% and 7.5% among a wide range of driving cycles. Fuel consumption at idle is 13% higher with AC on. MOVES underestimates the real-world FE with AC by 6%, on average. MOVES overestimates the AC effect on cycle-average FE ranging between 13.5% and 18.5% for real-world and MOVES default cycles, and between 11.1% and 14.5% for standard cycles.

Geospatial Variation of Real-World Tailpipe Emission Rates for Light-Duty Gasoline Vehicles

“…The emission rates of each vehicle were measured downstream of the three-way catalyst at the tailpipe. An OEM-2100 PEMS was used to measure tailpipe exhaust concentrations of CO 2 , HC, CO, and NO x at 1 Hz. ,,,, Battelle previously evaluated a similar model PEMS based on LDGV chassis dynamometer measurements . For CO 2 , CO, and NO x g/mile emission rates, the slopes of the parity plots between PEMS versus dynamometer varied from 0.92 to 1.05, indicating acceptable accuracy.…”

“…Since 2008, NC State University (NCSU) has measured real-world tailpipe fuel use and emission rates of 205 LDGVs on predefined study routes using Portable Emission Measurement Systems (PEMS). ,,,, The routes include a wide range of speed limits, acceleration, and RG. The vehicles represent a wide range of weight, engine size, emission standards, and other factors.…”

Switching on auxiliary devices in vehicular fuel efficiency tests can help cut CO2 emissions by millions of tons

“…7 Although many researchers indicate that AC could contribute to the fuel efficiency gap, [6][7][8][9] there are limited empirical investigations that have quantitatively examined increases in energy consumption due to AC usage. The few studies illustrating automobile AC's impact on overall energy consumption entail either simulation in labs [11][12][13] or real-world experiments based on small samples, e.g., the work of Weilenmann et al, 14 Liu et al, 15 and Khan and Frey, 16 which were conducted on 6 gasoline cars, 68 electric vehicles (EVs), and 205 gasoline cars, respectively. Due to limited sample sizes and car models, it is currently unclear to what extent the performance of AC systems can differ across various car models, such that a more accurate estimation of the potential to improve real-world fuel efficiency remains lacking.…”