Impact of idling on fuel consumption and exhaust emissions and available idle-reduction technologies for diesel vehicles – A review

•In this paper we reviewed the impact of diesel vehicles idling on fuel consumption and exhaust emission.•Fuel consumption and emissions during idling are very high compared to driving cycle.•The effects of various operating on fuel consumption and exhaust emission were discussed.•Available idle-reduction technologies impact on idling fuel consumption and emissions were discussed.•Idling reduction technologies reduce fuel consumption and emissions significantly. In order to maintain cab comfort truck drivers have to idle their engine to obtain the required power for accessories, such as the air conditioner, heater, television, refrigerator, and lights. This idling of the engine has a major impact on its fuel consumption and exhaust emission. Idling emissions can be as high as 86.4g/h, 16,500g/h, 5130g/h, 4g/h, and 375g/h for HC, CO2, CO, PM, and NOx, respectively. Idling fuel consumption rate can be as high as 1.85gal/h. The accessory loading, truck model, fuel-injection system, ambient temperature, idling speed, etc., also affect significantly the emission levels and fuel consumption rate. An increase in accessory loading and ambient temperature increases the emissions and fuel consumption. During idling, electronic fuel-injection systems reduce HC, PM, and CO emission, but increase NOx emissions compared with a mechanical fuel-injection system. An increase of idling speed increases fuel consumption rate. There are many systems available on the market to reduce engine idling and improve air quality and fuel consumption rate, such as an auxiliary power unit (APU), truck stop electrification, thermal storage systems, fuel cells, and direct fire heaters. A direct fire heater reduces fuel consumption by 94–96% and an APU reduces consumption by 60–87%. Furthermore, these technologies increase air quality significantly by reducing idling emissions, which is the reason why they are considered as key alternatives to engine idling.