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In last 10 years or so, a number of OEMs are designing vehicles with start-stop function to save energy and to reduce pollution. For these systems, the situations in which air-conditioning systems are used have been changing with a significant increase in adoption of idle-time reduction systems (no idling-system). Blower fan remains operating at idle condition while compressor stops in most cases for these systems. In this case, the air temperature at the vent outlets increases. The increase in the air temperature under range of thermal boundary conditions around the evaporator causes a concern of odor to occur. This paper describes and explains experimental studies on changes in heat and humidity at the air outlets according to the switching operation of compressor and root cause analyses of odor coming from air-conditioning system for vehicles with start-stop function.

Water drainage characteristics of an evaporator changes with the age of the vehicle. This is due to the fact that with time, a part of the hydrophilic coating washes off with the moisture that condenses over the evaporator core from the air-stream. Hence, the effectiveness of the evaporator for water drainage deteriorates with the age of the vehicle. At this condition more water is retained in the evaporator as the contact angle increases. Author has conducted experiments with evaporators from multiple vehicles from different OEMs. These evaporators were analyzed to determine the effectiveness of the hydrophilic coating as a function of time or vehicle age. This is the first paper in the open literature that deals with the vehicle mileage or vehicle age with the evaporator plate contact angle and surface coating of an evaporator.

Water drainage characteristics are dependent on the design of the evaporator: specifically the design of the fins and plates along with hydrophilic coating. A part of the hydrophilic coating washes off with the moisture that condenses over the evaporator core from the air-stream. Hence, water drainage characteristics of an evaporator changes with the vehicle mileage or the age of the vehicle. Since a part of the hydrophilic coating washes away, more water is retained within the evaporator at this condition. Hence, the effectiveness of the evaporator drainage deteriorates with the age of the vehicles. At this condition, the contact angle measured at the plate increases. Author has conducted an experimental study to measure the effectiveness of hydrophilic coating from evaporators taken out from arid (9 cores) and humid areas (16 cores) as a function of vehicle mileage or vehicle age. Contact angles and water retention were measured for a number of evaporators from different OEMs.

Tests were conducted with a laminate evaporator for an automotive application. The tests were conducted with HFO-1234yf as the working fluid on an AC system bench. A laminate evaporator from MY 2008 medium sized sedan was used for this investigation. Tests were first conducted with R-134a and were then repeated by maintaining each test condition by changing the working fluid from R-134a to HFO-1234yf. Charge determination tests were also conducted with the new refrigerant. The refrigerant was used as “drop-in” refrigerant in the existing system. All original OEM parts were used with the alternate refrigerant. Same TXV set-point and lubricant type and quantity was used with HFO-1234yf. The new refrigerant has advantages due to the refrigerant thermodynamic properties that helps reduce the pressure ratio. Detailed test results have been presented in this paper.

Experimental tests were conducted on a parallel flow condenser with HFO-1234yf as the working fluid on an AC system bench to determine average and local heat transfer coefficients during condensation of HFO-1234yf for mass flow rates that are typically encountered from idle to highway speeds (800 to 3000 rpms). A condenser from MY 2008 medium-sized sedan was used for this investigation. All original OEM parts were used with the alternate refrigerant. Same TXV set-point was used with HFO-1234yf. The magnitude of the measured heat transfer coefficient for condensation was found to be 8~12% lower in comparison to HFC-134a. The magnitudes of the pressure drop during condensation were of the same magnitude as HFC-134a system. The information from this investigation can be used to in the design of condensers for mobile air conditioning systems with HFO-1234yf as the working fluid.

In a recent study the author (Mathur, 2006) had conducted an experimental study by monitoring and collecting the tailpipe emissions (NOx, CO, HC) of the exhaust gases for automobiles, buses, and trucks at peak and off-peak hours for major roads and highways in Detroit metropolitan area. The current study focuses on the influence of the vehicle speed and ambient temperature on the amount of CO, HC and NOx entering into the vehicles' cabin in a controlled test environment. These tests have been conducted at CalsonicKansei North America's (CKNA) wind tunnel. Two sensors were installed in the vehicle to monitor outside and inside concentration of the above gases. The tests were conducted at a number of vehicle speeds to determine the influence on the amount of the gases entering into the cabin due to the response time of the actuator for the blower unit's air intake door.

Experimental tests were conducted on a parallel flow condenser with HFO-1234yf as the working fluid on an AC system bench. This refrigerant is being considered as an alternative refrigerant for mobile air conditioning systems (MACS) to address the global warming concerns. A condenser from MY 2008 medium sized sedan was used for this investigation. Tests were first conducted with R-134a and were then repeated by maintaining each test condition by changing the working fluid from R-134a to HFO-1234yf. The refrigerant was used as “drop-in” refrigerant in the existing system. All original OEM parts were used with the alternate refrigerant. Same TXV set-point was used with HFO-1234yf. Detailed test results have been presented in this paper.

An experimental investigation has been carried out to quantify the performance enhancements with a suction line heat exchanger (SLHX) in an AC system with HFO-1234yf as the working fluid. An off-the-shelf double pipe cross fluted SLHX is used for this investigation. System level bench tests are conducted with an AC system from a 2009 MY mid-sized sedan. The test results shows that the AC system performance with HFO-1234yf can be improve up to 8~9% in comparison to a baseline system without a SLHX.

Author has developed a correlation to predict flow boiling heat transfer coefficients for refrigerant evaporating in an automotive evaporator. This is a first correlation in the open literature for HFO-1234yf to predict heat transfer coefficients for automotive evaporator. The refrigerant mass flux was varied from 500 to 1200 kg/m2.s; heat flux was varied from 2 to 6.2 kW/m2; inlet refrigerant qualities from 0 to 40% and exit qualities of about 95%. The tests were conduct at 4.4 °C and the oil circulation ratio was maintained at 3%. Experimental data has been used with MINITAB software, Version 16.1.0 to develop this correlation. Multivariate nonlinear regression analysis has been done to develop this correlation. Experimental data along with refrigerant properties, hydraulic diameter that affects Reynolds number, Prandtl number and other appropriate variables have been used to develop this correlation. Details of the newly developed correlation have been presented in the paper.

The current investigation is focused on monitoring and collecting the tailpipe emissions (NOx, CO, HC) of the exhaust gases for automobiles, buses, and trucks. The experimental data has been collected to record the peak and off peak hour tailpipe gas concentrations levels for major roads and highways in Detroit metropolitan area. This was accomplished by mounting a sensor on the vehicle's cowl to record the concentration levels of the above gases. A second sensor was installed inside of the cabin to monitor the concentration levels of the above gases entering into the cabin due to the response time of the actuator for the blower unit's air intake door. The levels of the gas concentrations on Detroit metro highways are moderate to high in comparison to rural regions. The concentration levels are the worst on I-696 and North Western Highway10 inside of the tunnels and the areas where retaining walls are present on either sides of the highway.

Author has developed a correlation to predict condensation heat transfer coefficients for refrigerant condensation in an automotive parallel flow condenser. This is a first correlation in the open literature for HFO-1234yf to predict heat transfer coefficients for an automotive condenser. The system refrigerant mass flowrate was varied from 180 to 475 kg/hr; inlet refrigerant qualities from 1 to exit qualities of 0. The tests were conducted at an average condenser saturation temperature of 50°C and the oil circulation ratio was maintained at 3%.

Field tests were conducted on a late full sized sedan with the HVAC unit operating in both Recirculation and OSA modes to monitor build-up of the CO2 concentration inside the cabin and its influence on occupant’s fatigue and alertness. These tests were conducted during 2015 summer on interstate highways with test durations ranging from 4 to 7 hours. During the above tests, fatigue or tiredness of the occupants (including CO2 levels) was monitored and recorded at 30 min intervals. Based on this investigation it is determined that the measured cabin concentration levels reaches ASHRAE (Standard 62-1999) specified magnitudes (greater than 700 ppm over ambient levels) with three occupants in the vehicle. Further, the occupants did show fatigue when the HVAC unit was operated in recirculation mode in excess of 5 hours. Further details have been presented in the paper.

Performance of a parallel flow condenser is simulated by using hydrocarbons as the alternative refrigerants. The performance of the condenser is simulated with Propane (R-290), Isobutane (R-600a), and 50/50 mixture (by weight) of Propane and Isobutane. The performance is compared to a system with R-134a as the working fluid. For a given condenser heat rejection capacity, the refrigerant mass flow rates for hydrocarbon refrigerants are significantly lower than R-134a. However, the heat transfer coefficients are comparable in magnitudes to the base case (R-134a) which results in heat transfer rates that are very close to that of the base case. Hence, the simulated rate of heat transfer for hydrocarbon refrigerants is very close (within ±3%) to that of R-134a system. The pressure drop for hydrocarbon refrigerants are significantly lower in comparison to R-134a. The simulated thermal performance has been compared with the experimental test data obtained from the system bench.