As part of the 1997 Propane Vehicle Challenge, a team of twelve UTEP students converted a 1996 Dodge Grand Caravan with a 3.3 L V6 engine to dedicated Liquefied Petroleum Gas (LPG) operation according to the 1997 Propane Vehicle Challenge (PVC) competition rules (16). The 1997 UTEP team developed an LPG liquid phase port fuel injection (LPP-FI) system for the minivan. The UTEP design strategy combines simplicity and sound engineering practices with the effective use of heat resistant materials to maintain the LPG in the liquid phase at temperatures encountered in the fuel delivery system.
The team identified two options for fuel storage with in-tank fuel pumps. The competition vehicle incorporates a five-manifold eight inch diameter Sleegers Engineering LPG tank fitted with a Walbro LPTS in-tank pump system, providing a calculated range of 310 city miles and 438 highway miles. UTEP team members collaborated with Sleegers Engineering for the tank design, providing input on tank size, location, and Walbro LPTS flange specification. An independent fuel delivery and return system was developed to provide equal fuel delivery to each cylinder, and to eliminate heat transfer problems associated with a single metallic fuel rail. Care was taken to minimize the number and size of metallic fittings in the fuel delivery and return system so as to minimize heat transfer to the LPG. Prototype Siemens DEKA II LPG fuel injectors are housed in in-house manufactured Nylon-6 injector holders placed in the original fuel injector locations with only slight modification to the intake manifold. To remove heat transferred to the LPG during fuel delivery, a novel electronically-controlled thermoelectric heat pump heat exchanger was developed and placed in the fuel return line. The stock Powertrain Control Module (PCM) is retained for all engine management. To account for LPG, the MAP sensor voltage is modified prior to being sent to the PCM. This serves to decrease the amount of fuel delivered per injection and increase the spark timing advance, both of which are beneficial for LPG. A resistor is placed in parallel with the engine coolant temperature sensor to eliminate cold start fuel enrichment, which is not required for LPG.
The UTEP vehicle provides an excellent demonstration of the benefits derived from the LPP-FI system. Although the system could be further optimized for dedicated LPG (e.g. increased compression ratio, optimized EGR schedule, optimized transmission shift schedule, etc.), our system demonstrates benefits derived from a low-cost conversion of a gasoline vehicle, which is of benefit to OEM vehicle manufacturers and the aftermarket alternative fuels industry.