Strategies for Low Engine Speed Torque Enhancement of Natural Gas Engine Used for Commercial Vehicles: Observations with Compression Ratio

Abstract

Since many years diesel engines are powering commercial vehicles. Of late, governments are promoting the use of natural gas (NG) as a fuel for such vehicles to reduce pollution. Thereafter, natural gas engines have witnessed faster development, especially for use in commercial vehicles. City bus is probably the most common NG commercial vehicle, dedicated to ferry passengers across the city. Some places impose a safety speed limit on such vehicles considering local traffic conditions. Thus, a typical scenario faced by such vehicles includes low drive speeds, high loads, frequent halts for passenger pick up and drop, signals, etc. Such vehicles thus need high torque at low engine speeds to  manage these daily occuring conditions. Aim of this paper is to enhance torque at low-engine speed zone. Number of options such as the use of a turbocharger, direct injection of fuel, variable valve actuation, programmable waste-gates, etc. can help to realize higher engine outputs. The intent here is to study the effect of compression ratio and understand the extent of change in torque in engine low-engine speed region. Current study consists of modelling a reference commercial vehicle engine of six cylinders. A virtual model is built and its ability to represent actual engine performance from testbed is verified. Further, such model undergoes iterations of change in compression ratio and different parameters are studied for their relation with torque.