Idle Reduction Technologies

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Abstract: A number of control technologies have been commercialized to reduce idle emissions and fuel consumption. The most important types of technology include automatic engine shut-down and start-up systems, battery powered cabin heating and air conditioning devices, diesel fired heating systems, auxiliary power units (APU), and truck stop electrification.

Driving Factors

The development of idling reduction technologies (IRT) for new and in-use vehicles has been stimulated by idle reduction programs, regulatory initiatives, and the demand for increased vehicle fuel efficiency. Regulations limiting idling and/or idling emissions are being increasingly adopted by regulatory bodies. California has in place regulations to limit idling of school buses at schools, and to reduce idling emissions from new and in-use trucks beginning in 2008. Also, the US EPA Tier 3/4 rule for locomotives includes provisions to eliminate emissions from unnecessary locomotive idling. Idle reduction programs—ranging from administrative limits on the allowed idling time to the use of advanced idle reduction technologies—are also being implemented by many local authorities worldwide. In the USA, states can claim emission credits in their state implementation plans (SIP) for idle emission reductions from trucks [1317] and from switch yard locomotives [1318].

Some idle reduction regulations also establish idle emission standards. New vehicles certified to the idle emission standards are exempted from limits on the allowed idling time and/or other idle reduction requirements. An example of this approach is the California regulation limiting idling in heavy-duty commercial vehicles to 5 minutes. The regulation provides an exemption for engines that are certified to emit no more than 30 g/h NOx at idle and that do so by not increasing CO, PM or NMHC.

Beginning with model year 2008, manufacturers are offering engines that meet the California idle NOx emission standard. For example, Volvo introduced an optional low NOx idle (LNI) feature on its D11, D13, and D16 heavy-duty engines. Volvo’s LNI involves idling at a low speed of 700 rpm to reduce fuel consumption, while also employing a low level of EGR to reduce NOx. The engines were designed to allow idling for extended periods of time.

Classification of Technologies

The existing commercial technologies to reduce idling and idle emissions can be classified as follows:

Figure 1 shows the adoption rate of some of these technologies by US trucking fleets [3563].

Solid oxide fuel cells (SOFC) that are fueled by diesel fuel have also been under development and show potential to be used as APUs [1769].

A comprehensive listing of technologies for idle emission reduction from highway trucks and from locomotives has been compiled by the US EPA [1312][3567].