The design, development and optimization of an internal combustion engine require the application of a modern sophisticated analysis tool. In addition to experimental work, numerical calculations are now necessary to provide an insight into the complex in-cylinder process. The combustion process and its emission characteristics in a compressed natural gas direct injection engine were analyzed and investigated. The numerical studies were performed on a single cylinder of a 1.6-liter engine running at wide open throttle. The grid generation was established through an embedded algorithm for moving mesh and boundary in order to provide a more accurate transient condition. The combustion process was modelled with the eddy break-up model of Magnussen for unpremixed or diffusion reaction with three global reaction scheme. The computational fluid dynamics (CFD) simulations at two baseline conditions are carried out to examine the fluid flow, air-fuel mixing formation, combustion process, carbon monoxide emission distribution as well as NO emission formation occurred inside engine cylinder. The CFD results were compared with the experimental data and showed a very good agreement for two baseline conditions. A set of parametric studies were carried out by varying the timings of start of injection (SOI) and start of ignition (SI). The examined engine performance is in-cylinder pressure, while the considered emissions to be minimised are CO and NO levels. In order to study the effect of injection timing, the SOI timing was varied from 120o-140o with fixed ignition timing at 19o bTDC. On the other hand, SI timing was positioned from 15o -23o bTDC with fixed SOI timing for studying its influences. The CFD results indicated that slightly retarded SOI and SI timing can be chosen to reduce CO and NO levels while increasing engine performance.

Natural gas compressor stations in gas transmission industries cause to increase gas pressure and discharge to gas transmission pipeline. Air coolers in compressor station, have high electrical energy consumption and pressure drop. In this investigation, the application of heat pipe heat exchangers (HPHE) in a case study of the gas compressor station is evaluated to use instead of air coolers. The result of the investigation shows that applying 620 heat pipes with a 50% filling ratio, working fluid R134 and arranged triangularly, can reduce the compressed natural gas temperature. Energy performance analysis shows that using this method improves total, thermal, and electrical energy performance indicators (3%, 2.4 %, and 78%, respectively). Also simulating process demonstrate that using HPHE cause to save 1,115,000 SCM fuel in gas turbine and 3,800 MWh electrical saving in air coolers. In addition, results show with using HPHE 2,615,000 $ cost saving is available and project payback period value less than 1 year evaluated, and avoiding 1652 ton CO2 emission estimated annually.

Application of Compressed Natural Gas (CNG) in diesel engines has always been important, especially in the field of automotive engineering. This is due to easy accessibility, better mixing quality and good combustion characteristics of the CNG fuel. In this study the application of CNG fuel along with diesel oil in a heavy duty direct-injection automotive diesel engine is experimentally investigated. In order to convert a diesel engine into a diesel-gas one, the so called" mixed diesel-gas" approach has been used and for this purpose a carbureted CNG fuel system has been designed and manufactured. For controlling quantity of CNG, the gas valve is linked to the diesel fuel injection system by means of a set of rods. Then, the dual-fuel system is adjusted so that, at full load conditions, the quantity of diesel fuel is reduced to 20% and 80% of its equivalent energy is substituted by CNG fuel. Also injection pressure of pilot jet is increased by 11.4%. Performance and emission tests are conducted under variation of load and speed on both diesel and diesel-gas engines. Results show that, with equal power and torque, the diesel-gas engine has the potential to improve overall engine performance and emission. For example, at rated power and speed, fuel economy increases by 5.48%, the amount of smoke decreases by 78%, amount of CO decreases by 64.3% and mean exhaust gas temperature decreases by 6.4%.