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 have been 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 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. A compendium of idling regulations for the USA can be found elsewhere [6616].

Pressure to limit idling also arises from GHG regulations. Unless there is a pressing need to idle a vehicle, shutting down the engine during idling—especially for vehicles where long periods of idling can occur—is often a cost-effective way to reduce CO₂ emissions.

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.

Types of Technologies

Overview

A range of technologies to reduce the amount of engine idling in vehicles are available. Some of these technologies are applicable to vehicles while the vehicle is driven during normal operation while others are primarily intended to minimize the amount of idling during times when the vehicle is parked but there is a need to control cabin temperature, engine temperature and/or charge the vehicle’s batteries [6618][6619].

Figure 1 shows the adoption rate of some of these technologies by US regional and long-haul trucking fleets [3563][6617].

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

Neutral Idle

Neutral idle automatically switches an automatic transmission into neutral when the vehicle comes to a stop while driving and back into drive when pulling away. This disengages the torque converter and reduces the load on the engine when the vehicle is stopped. While the engine still idles, it does so with a lower parasitic load and thus emissions and fuel consumption are reduced. For some heavy-duty vehicles, fuel/CO₂ reductions of about 5% are possible.

Engine Start/Stop

Engine start/stop goes one step beyond neutral idle and shuts the engine off when a vehicle comes to a stop while driving and restarts it when pulling away. While common in light-duty passenger cars and many commercial vehicles, application to some types of commercial vehicles poses challenges. Line-haul trucks would see little benefit from this technology due to their typical operating cycle while refuse vehicles could benefit from this technology but would require a very robust system due to the high frequency of use and the need to maintain other vehicle functions when the vehicle is stopped.