The economic assessments for the use of compressed natural gas as fuel for several types of diesel vehicles, rarely pick up, non-fixed route truck and private truck, were studied. It is noted that two main technologies of diesel natural gas vehicle (NGV), i.e. dedicated retrofit and diesel dual fuel (DDF), were considered in this work. It was found that the dedicated retrofit needs higher investment costs than dual fuel, but can achieve higher diesel saving than dual fuel. In detail, the payback period of dual fuel non-fixed route truck was found to be identical to dual fuel private truck both in the cases of 6 wheel and 10 wheel, while dedicated retrofit non-fixed route truck and private truck are also identical and have longer pay back period than dual fuel due to its higher conversion costs. This work also presents the emissions released from all types of engines especially green house gas CO2 . It was found that, in the case of light duty diesel i.e. pickup truck, dedicated retrofit emitted high level of CO2 than both dual fuel and conventional diesel engines. For heavy duty i.e. non-fixed route truck and private truck vehicles, dedicated retrofit emitted a lower level of CO2 than normal diesel engine. Other pollutants from engine emission, i.e. hydrocarbon (HC), nitric oxide (NOx), carbon monoxide (CO) and particulate matter, (PM) were also observed. The results indicated that, in the case of light duty diesel, dedicated retrofit engine emits higher levels of HC and CO than diesel engine; in contrast, it emits lower level of NOx and PM than diesel and dual fuel. Dual fuel emits HC and CO higher than diesel and dedicated retrofit but emits lower level of NOx and PM than diesel. Lastly, for heavy duty diesel, it was demonstrated that non-fixed route truck and private truck heavy duty dedicated retrofit have potential to reduce emissions of HC, NOx , CO and PM when compared to normal heavy duty diesel. Engine efficiencies under dual fuel and dedicated retrofit operation were lower than that of the normal diesel engine.
