Particle Number and Size Distribution of Emissions during Light-Duty Vehicle Cold Start

Abstract

Vehicle emissions during cold start are known to be significantly higher than after optimal vehicle operating temperatures are reached. There are limited data, however, on particle number and size distributions during cold start. Cold-start tailpipe emissions from a 1999 Toyota Sienna minivan were quantified at ambient temperatures between 20°C and 37°C using a novel system, the total onboard tailpipe emissions measurement system (TOTEMS), assembled to quantify the full suite of exhaust emissions from light-duty vehicles. TOTEMS particle number distributions were measured from 5.6 to 562 nm using an engine exhaust particle sizer (EEPS) and total 3- to 3,000-nm particle counts were measured using an ultrafine condensation particle counter (UCPC) with 1-s temporal resolution during cold start and warm-up driving. Second-by-second particle number distributions from five cold-start emissions tests showed similar particle emissions patterns, allowing for three different cold-start phases to be identified based on particle number emissions behavior. Cold-start duration ranged from 165 to 230 s and increased with decreasing ambient temperature. Different particle sizes during each phase were emitted for different lengths of time, with the most abundant particles in the nanoparticle (diameter <50 nm) range. The mean particle number distributions showed more than 99% of total particle number below 100 nm. Concentrations of ultrafine particles (<100 nm) during cold start were at least 10 to 100 times (EEPS), and as much as 1,000 times (UCPC), above hot-stabilized idle emissions. Observations also suggest the presence of tiny particles below 6 nm during cold start.

Onboard, Real-World Second-by-Second Particle Number Emissions from 2010 Hybrid and Comparable Conventional Vehicles

“…As described in more detail elsewhere (1,23), a suite of 20 instruments and accompanying data acquisition were assembled to collect second-by-second vehicle operation and tailpipe emissions data as test vehicles operate in the real world. This package, the total onboard tailpipe emission measurement system (TOTEMS), collects emission data on particle number concentration and size distributions as well as 32 exhaust gas species.…”

“…The number of hybrid ICE restarts correlated well with the magnitude of cumulative and average total particle number concentrations. Thus, it is likely that at every ICE restart event the hybrid vehicle experienced a commanded enrichment event analogous to that experienced during ICE cold starts, where up to order-of-magnitude increases in particle number emissions have been observed for light-duty vehicles (16,23,25). There is also an instantaneous load applied to the hybrid vehicle ICE at restart, which could further enrich conditions in the engine and increase particle number emissions.…”

Second-by-Second Characterization of Cold-Start Gas-Phase and Air Toxic Emissions from a Light-Duty Vehicle

“…Cold start was defined by an engine soak time of at least 12 h at ambient temperature before engine ignition. Particle number distributions for these cold starts are presented in a separate paper (10).…”

“…Additionally, low-emitting vehicles (typical of the most recent model year vehicles) require instrumentation capable of lower detection limits, compelling development of new PEMS. This study investigates use of FTIRs for onboard tailpipe emissions, alongside particle sizing and counting instrumentation (10).…”

Characterization of Real-World Particle Number Emissions during Reignition Events from a 2010 Light-Duty Hybrid Electric Vehicle

“…As part of a larger study designed to improve understanding of vehicle emissions under real-world driving conditions (24,25), this study (a) developed a new framework for HEV ICE operating mode based on analysis of second-by-second PN emissions and engine activity occurring during reignition events, (b) quantified the magnitude of PNER from reignition events compared with stabilized HEV and CV operation, and (c) examined the differences between ICE operation and PNER across three roadway types (urban, rural, and freeway).…”