Question

Problem 2.

A novel gaseous hydrocarbon fuel CxHy is proposed for use in spark-ignition engines. A sample analysis of this fuel revealed that its molecular weight is 140 kg/kmol and its molar H/C ratio is 2. In order to evaluate some of its properties, the fuel was burned with stoichiometric atmospheric air in a constant pressure, steady-flow reactor. The fuel and air entered the reactor at 25 C, and the products of complete combustion were cooled to 25 C. At the exit condition, water in the products was liquid. It was measured that the heat given off during the process to the cooling system of the reaction was 47.5 MJ/kg of fuel.

a) Determine the fuel formula.

b) What does that heat given-off to the cooling system of the reactor represent?  

c) Determine the lower heating value of the fuel

d) Determine the enthalpy of formation of the fuel at 25 C.

Problem 3.

The fuel of problem 2 above was used to run a spark-ignition engine in a laboratory environment simulating the atmosphere of planet Mars. The oxidizer was composed of (O2 + 3CO2). Stoichiometric amounts of oxidizer and fuel entered the engine at 25?C, while combustion products in the exhaust manifold were at an average temperature of 1000 K. Only products of complete combustion were found in the exhaust. It was measured that the engine produced a power of 2 kW while the heat transfer rate to the surroundings was 1 kW.

a) Determine the mass flow rate of the fuel supplied to the engine.

b) Determine the fuel conversion efficiency of the engine when operated with the proposed fuel.

Answer 1