Cold start performance

The vast majority of propane fuel systems used on light-duty vehicles to date have been of the mechanical-control type that meter propane in proportion to the amount of air used by the engine (air-valve and venturi-type mixers ). While these systems work well, their capabilities have been overshadowed by gasoline fuel injection systems and often lag behind gasoline systems in terms of acceleration, driveability, and cold-start performance. Chrysler Canada and one European equipment manufacturer offer liquid propane injection systems that are direct analogs to gasoline port fuel injection systems. These systems should have inherent performance advantages compared to the vaporized propane fuel systems. 

Data are not widely available, but it is likely that liquid propane fuel systems should have improved vehicle acceleration relative to vaporized propane fuel systems. Vaporization of the propane would occur right in the intake port, cooling the intake air and regaining some of the volumetric efficiency loss that fully vaporized propane systems experience. More precise control of propane metering, especially during acceleration, should also improve vehicle acceleration performance. Such propane fuel systems should also have excellent driveability and cold-start performance the same or better than gasoline vehicles. 

Very few heavy-duty propane vehicles have been developed and put into use therefore, a database of knowledge about their performance characteristics does not exist. However, their characteristics should be similar to the relative differences between natural gas heavy-duty vehicles and their diesel engine counterparts. If this supposition holds true, heavy-duty propane vehicles should have similar or better power, the same or better driveability, and better cold-start performance compared to the same vehicle with a diesel engine. (Unlike light-duty vehicles, heavy-duty propane vehicles should have better cold-start performance compared to diesel engines because of the many cold-start challenges diesel engines face.)... 

Combining Eqs. (3) and (4), we can conclude that product water of approximately 1 mg/cm2 is a criterion for successful self-startup. As shown with Eqs. (3) and (4), the temperature increase is proportional to the product water, and therefore, the product water from the fuel cell operation, Am o, is considered a quantitative index to measure the cold-start performance. 

Wang15 investigated heat and mass transport and electrochemical kinetics in the cathode catalyst layer during cold start, and identified the key parameters characterizing cold-start performance. He found that the spatial variation of temperature was small under low current density cold start, and thereby developed the lumped thermal model. A dimensionless parameter, defined as the ratio of the time constant of cell warm-up to that of ice... 

Recently Meng17 developed a transient, multiphase, multidimensional PEFC model to elucidate the fundamental physics of cold start. The results showed the importance of water vapor concentration in the gas channels, which implies that large gas flow rates benefit cold-start performance. They also found that ice growth in the cathode catalyst layer during cold start was faster under the land than under the gas channels, and accumulated more at the interface between the cathode catalyst layer and GDL. 

Figure 2. Effect of initial water content X in the membrane on cold-start performance. The environmental temperature is —30°C. (reproduced with permission from Tajiri et al.18 )...

In light of the importance of water storage in partially dry membranes, it is instructive to correlate the cold-start performance quantified by product water (mElo, mg/cm2) with the membrane water uptake potential (Ak) defined as ... 

The cold-start performance for two different purge modes are directly compared in Fig. 11 for -20°C startup with various initial... 

Thus, it seems the short-purge cold start does not fully utilize the cold-start capability of MEA. Deeper understanding of the purge mechanisms will help to greatly improve short-purge cold-start performance. This is the motivation of the next section. 

Fundamental mechanisms of this relaxation phenomenon remain unknown and need future investigation. However, correlating the T-compensated HFR after relaxation with that after purge is of practical interest, because the initial membrane water content critically important for PEFC cold-start performance corresponds to the HFR after relaxation (during cool down), not the FIFR immediately after purge. For this reason, an empirical correlation is attempted between the HFR after purge and that after relaxation, as shown in Fig. 21. It can be seen that a reasonable correlation exists over a... 

The correlation shown in Fig. 21 provides a practical means to estimate the HFR or membrane water content as the important input to evaluate cold-start performance. That is, one can estimate the HFR after purge from Eq. (10) based on the purge conditions, and subsequently correct for HFR relaxation using Fig. 21. Based on the HFR value after relaxation or prior to cold start, one can use the analytical models and performance data developed in previous work to estimate the cold-start performance. 

Honda FCX with breakthrough fuel cell stack proves its cold-start performance capabilities in public test. Torrance, CA, 27 Feb, 2004. http //world.honda.eom/news/2004/4040227FCX/... 

Jiao K and Li X (2009), Effects of various operating and initial conditions on cold start performance of polymer electrolyte membrane fuel cells, International Journal of Hydrogen Energy, 34,8171-8184. 

Ura J A, Girard J, Cavataio G, Montreuil C, Lambert C (2009) Cold Start Performance and Enhanced Thermal Durability of Vanadium SCR Catalysts. SAE Technical Paper 2009-01-0625... 

Cold start performance needs to be carefully managed, because the customer expects the same service from the vehicle regardless of the weather conditions. The technical specifications for automobiles for such au application prescribe the capacity to start up in less than 30 seconds at -30°C. The simplest solution, which is totally accepted in Canada, for instance, for conventional vehicles, is to use a block heater , which includes electrical coverings or heating resistances that are plugged into the electrical grid. More transparent solutions from the customers point of view are under investigation to overcome this difficulty. 

Improved engine wear protection Extended oil drain interval Excellent cold starting performance Improved fuel economy Reduced oil consumption... 

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