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Black carbon (BC) is considered the second largest anthropogenic climate forcer, but the radiative effects of BC are highly correlated with its combustion sources. On-road vehicles are an important source of anthropogenic BC. However, there are major uncertainties in the estimates of the BC emissions from on-road light-duty passenger vehicles (LDPVs), and results obtained with the portable emissions measurement system (PEMS) method are particularly lacking. We developed a PEMS platform and evaluated the on-road BC emissions from ten in-use LDPVs. We demonstrated that the BC emission factors (EFs) of gasoline direction injection (GDI) engine vehicles range from 1.10 to 1.56 mg·km−1, which are higher than the EFs of port fuel injection (PFI) engine vehicles (0.10–0.17 mg·km−1) by a factor of 11. The BC emissions during the cold-start phase contributed 2%–33% to the total emissions. A strong correlation (R2 = 0.70) was observed between the relative BC EFs and average vehicle speed, indicating that traffic congestion alleviation could effectively mitigate BC emissions. Moreover, BC and particle number (PN) emissions were linearly correlated (R2 = 0.90), and compared to PFI engine vehicles, the instantaneous PN-to-BC emission rates of GDI engine vehicles were less sensitive to vehicle-specific power-to-velocity (VSPV) increase in all speed ranges.

In this paper, the real driving particle number (PN) emissions from two China-6 compliant hybrid electrical vehicles (HEVs) were measured using a certification-level portable emission measurement system (PEMS) and strict adherence to the regulatory procedures for real driving emission (RDE) testing. The results show that the trip-averaged PN emission factors for the port fuel injection (PFI) HEV and the gasoline direct injection (GDI) HEV were 1.15E+12 and 1.71E+12#/km respectively, much higher than the engine-only counterparts and failing the existing RDE limits. Enriched air-fuel mixtures and probably lowered catalyst conversion efficiencies as a result of more frequent engine stop-and-goes of the HEVs are found to be the underlying reasons for the extra PN emissions. The test results also suggest the necessity to amend the power management strategy currently widely used in HEVs to deal with the PN issue.

Light-duty gasoline vehicles have drawn public attention in China due to their significant primary emissions of particulate matter and volatile organic compounds (VOCs). However, little information on secondary aerosol formation from exhaust for Chinese vehicles and fuel conditions is available. In this study, chamber experiments were conducted to quantify the potential of secondary aerosol formation from the exhaust of a port fuel injection gasoline engine. The engine and fuel used are common in the Chinese market, and the fuel satisfies the China V gasoline fuel standard. Substantial secondary aerosol formation was observed during a 4–5 hr simulation, which was estimated to represent more than 10 days of equivalent atmospheric photo-oxidation in Beijing. As a consequence, the extreme case secondary organic aerosol (SOA) production was 426 ± 85 mg/kg-fuel, with high levels of precursors and OH exposure. The low hygroscopicity of the aerosols formed inside the chamber suggests that SOA was the dominant chemical composition. Fourteen percent of SOA measured in the chamber experiments could be explained through the oxidation of speciated single-ring aromatics. Unspeciated precursors, such as intermediate-volatility organic compounds and semi-volatile organic compounds, might be significant for SOA formation from gasoline VOCs. We concluded that reductions of emissions of aerosol precursor gases from vehicles are essential to mediate pollution in China.

Gasoline direct injection (GDI) vehicles are up against the great challenge of particulate emissions, which were mandatorily constrained by the China-6 emission standard. Given the worldwide fuel transition from gasoline to gasoline/ethanol blends, it is important to discuss the effects of ethanol and aromatic contents on particulate emissions of GDI vehicles. In this work, 10% volume of ethanol was added into China-6b gasoline replacing C8 (carbon atoms = 8) alkanes (E10), and the specific aromatic compounds in E10 fuels were adjusted under holding total aromatic content. As there was no limit on individual aromatic compounds in the gasoline standard, the effects of aromatic compounds were investigated over the worldwide harmonized light-duty test cycle (WLTC) with engine cold-start and hot-start at room and low temperatures. For GDI vehicles, the results showed that ethanol substituting part of C8 alkanes in gasoline increased the particulate number (PN) but decreased particulate mass (PM) emissions. For vehicles using the combined port fuel injection (PFI)/GDI injection systems, the PM and PN emissions climbed. Aromatic compositions significantly impacted the particulate emissions. With the concentrations of heavy aromatics increased, PM and PN emissions of both GDI and combined-injection vehicles were shown to multiply.

There has been a substantial increase of the number of direct injection spark-ignition (DISI) engines in the last decade as they can achieve much better efficiency than port fuel injection (PFI) engines. With direct injection (DI) system, engines tend to shift from the larger one to the smaller one coupled with turbocharger, namely engine downsizing. Because of the downsizing, the modern DISI engines are more sensitive to knock. Since knock is correlated to the burning rate of a combustion cycle and the burning rate can be varied significantly due to cycle-by-cycle (CBC) variation, one of the recent study on DISI engines is focused on the correlation between CBC variation and knock. Furthermore, as burning rate, CBC variation, and knock are all the functions of in-cylinder pressure, there should be a correlation among them. In this work, such correlation is studied experimentally by using a PFI and two DISI engines. From the statistical analysis, it has been found that CBC variation and burning rate are linearly correlated. It also has been found there is a linear relationship between knock and burning rate. By connecting the relationship between CBC variation and burning rate to the relationship between knock and burning rate, the relationship between knock and CBC variation is developed. Knock tendency increases with increasing CBC variation, which is attributed to the nonlinear relationship between the maximum in-cylinder pressure ( p max ) and net indicated mean effective pressure (NIMEP). By using the model of limited-pressure cycle with isentropic compression and expansion, it has been demonstrated that p max increases exponentially with increasing NIMEP.

Hydrogen cyanide (HCN) is considered a marker for biomass burning emissions and is a component of vehicle exhaust. Despite its potential health impacts, vehicular HCN emissions estimates and their contribution to regional budgets are highly uncertain. In the current study, Proton Transfer Reaction-Time of Flight-Mass Spectrometry (PTR-ToF-MS) was used to measure HCN emission factors from the exhaust of individual diesel, biodiesel and gasoline vehicles. Laboratory emissions data as a function of fuel type and driving mode were combined with ambient measurement data and model predictions. The results indicate that gasoline vehicles have the highest emissions of HCN (relative to diesel fuel) and that biodiesel fuel has the potential to significantly reduce HCN emissions even at realistic 5% blend levels. The data further demonstrate that gasoline direct injection (GDI) engines emit more HCN than their port fuel injection (PFI) counterparts, suggesting that the expected full transition of vehicle fleets to GDI will increase HCN emissions. Ambient measurements of HCN in a traffic dominated area of Toronto, Canada were strongly correlated to vehicle emission markers and consistent with regional air quality model predictions of ambient air HCN, indicating that vehicle emissions of HCN are the dominant source of exposure in urban areas. The results further indicate that additional work is required to quantify HCN emissions from the modern vehicle fleet, particularly in light of continuously changing engine, fuel and after-treatment technologies.

The effects of n-butanol/coal to liquid (CTL) dual fuel combustion mode on combustion and emissions characteristics were experimentally investigated at medium load. The CTL was produced by the Fischer-Tropsch process and the N-butanol was obtained by the biological fermentation. The optimized combustion boundary conditions mainly include n-butanol ratio, EGR rate and start of injection (SOI). The results showed that the premixed combustion ratio (PCR) of CTL is lower than the conventional diesel, which is beneficial to reduce the peak value of in-cylinder pressure and rate of pressure rise (ROPR). Port fuel injection of n-butanol improves the homogeneity of the mixture gas, which is contributing to increasing the PCR, shortening the combustion duration, thereby suppressing the generation of particles and improving the volumetricity of combustion. Introducing EGR effectively suppresses the excessive ROPR caused by the pre-injection of n-butanol and broadens the range of n-butanol premixed fraction. In the comparison of pure CTL mode, combining with the suitable EGR rate and SOI, the combustion mode of n-butanol/CTL dual fuel can simultaneously reduce NOx and particulate emissions. Among them, a higher n-butanol ratio needs to be combined with a higher EGR rate to obtain a better comprehensive emission performance, and increasing the n-butanol ratio promotes the conversion of particulate to nuclear mode. After optimization of the combustion boundary conditions, the NOx emission of the n-butanol/CTL dual fuel mode at the n-butanol ratio of 30% is reduced by 49.5%, and the particulate matter emission is reduced by 40.9%, relative to the pure CTL mode.

A chassis dynamometer study was conducted to compare the characteristics of particle emissions from a port fuel injection (PFI) and a gasoline direct injection (GDI) car, both of which comply with Euro 4 exhaust emission standards. Experiments were carried out over the New European Driving Cycle (NEDC), the ECE–15 segments, the period from 0 to 49 s within the NEDC procedure (FSE) and the Extra Urban Driving Cycle segment. Exhaust particles were characterized in terms of the particle number, surface area, volume and size distributions between 30 nm and 1 μm. Under the NEDC, the GDI car had particle emissions weighted by particle number, surface area and volume that were 56–2 739% higher than the emissions from the PFI car in the range of particle size measured, and the particle number, volume and surface area emissions per km for the GDI car are respectively 5.3, 9.0 and 14.6 times higher than those for the PFI car. Among the testing conditions employed, the highest concentrations of average particle number, surface area and volume were found in the FSE, and the particle number, surface area and volume for the GDI car were respectively 9.5, 33.2 and 39.8 times higher than those for the PFI car. Moreover, the peak of the particle size distributions for the PFI car was toward a smaller size, while that for the GDI was toward a larger size, indicating that particles emitted by the PFI car are much smaller than those emitted by the GDI car.

Frequent backfire can occur in inlet port fuel injection hydrogen internal combustion engines (HICEs) when the equivalence fuel–air ratio is larger than 0.56, thus limiting further enhancement of engine power. Thus, to control backfire, an inlet port fuel injection HICE test system and a computational fluid dynamics model are established to explore the factors that cause backfire under high loads. The temperature and the concentration of the gas mixture near the intake valves are among the essential factors that result in backfire. Optimizing the timing and pressure of hydrogen injection reduces the concentration distribution of the intake mixture and the temperature of the high-concentration mixture through the inlet valve, thus allowing control of backfire. Controlling backfire enables a HICE to work normally at high equivalence fuel–air ratio (even beyond 1.0). A HICE with optimized hydrogen injection timing and pressure demonstrates significant enhancement of the power output.

To reduce the cyclic variation is an effective way to improve the fuel economy and combustion of spark ignition engines. In this paper, the effect of exhaust gas recirculation (EGR), compression ratio and boost pressure on cyclic variation was investigated by means of both experiments and simulation for a port fuel injection (PFI) engine. The mechanisms of these effects were analyzed by computational fluid dynamics (CFD) tools. A Ricardo E6 PFI engine was used as the experimental prototype. The experiments were performed with six EGR ratios, three compression ratios and two boost pressures for a given equivalence ratios. The experiments were operated with the same parameters as that of the simulation. Results showed that the simulation work agree well with the experiment. Both simulation and experiment results showed that an increase of EGR ratio will increase cyclic variation for its lower laminar flame speed. However, the combination of EGR with either an appropriate compression ratio or boost pressure can achieve a relatively low cyclic variation.

In this work, an experimental study on the effects of the impingement geometry, the cross-flow intensity and the wall temperature on the characteristics of an impinging port fuel injection (PFI) spray was conducted. The transient development of the impinging spray was recorded by a high-speed camera with Mie scattering. Based on the high-speed images, the spray tip penetration (S) and the impinged spray height (Hw) were obtained. The results show that with the increase of the impingement distance (Lw), S increases and Hw decreases at the same time after the impingement. As the impingement angle (θw) increases, S decreases while Hw first increases and then decreases. With the increase of the cross-flow velocity (Uc), less part of the spray impinges onto the wall, and S significantly increases. As the wall temperature (Tw) rises, S does not show much variation. However, Hw increases gently for Tw lower than 420 K, and it increases sharply for Tw higher than 420 K due to the Leidenfrost mechanism. The effects of the above factors (Lw, θw, Uc, Tw) on S and Hw were finally evaluated and compared through the introduction of a contribution index.

The cycle variation characteristics of a port fuel injection hydrogen internal combustion engine (PFI-HICE) have been extensively investigated. The covariance of indicated mean effective pressure (COV imep ) is the best parameter for evaluating the cycle variations in the PFI-HICE. COV imep decreases as fuel–air ratio increases from 1000 to 5500 rpm, and engine speed minimally affects COV imep . The effect of ignition advance angle on COV imep is determined by fuel–air ratio. The ignition advance angles that correspond to the minimum COV imep of the PFI-HICE decrease as fuel–air ratio increases. The effect of ignition advance angle on COV imep diminishes as fuel–air ratio increases. The COV imep of the PFI-HICE rapidly decreases as throttle increases when the throttle is less than 20%. Injection timing only slightly affects COV imep under high-speed conditions, and COV imep increases when hydrogen is injected in intake periods under low-speed conditions. These results indicate that studying COV imep improves the stability of PFI-HICEs.

As an internal combustion engine fuel, hydrogen had been acknowledged by international auto industry to be a possible practical and economical fuel for automobile in the future. Port fuel injection is currently considered as the easiest way for hydrogen-powered vehicle application. As the key component of hydrogen system, the performance of hydrogen injector significantly influences the characteristic of the mixture before injection into the cylinder. However, current hydrogen injector system using one injector per cylinder is not capable of meeting the flow demand. To investigate the injector's flow characteristics and find a method of improving the injector's flux, a calibration test stand was designed for gas injectors that can exactly calibrate the injector's flow characteristics under injection pressure from 0.2 MPa to 0.45 MPa and injection duration from 1 ms to 10 ms. The minimum injection duration that enables the injector to work steadily was found to increase from 1.8 ms to 2.1 ms, which must be considered in idling speed. In addition, a hydrogen injector model was established using a one-dimensional simulation software. The effect of the structure parameters of the hydrogen injector on the flow characteristics was studied after verification and validation of the model with test data. By comparing the test and the calculation results, the flow area between the armature and the seal was established to have the largest effect on the injector's flow characteristics, and larger flux can be achieved by optimizing the related parameters of the injector. Therefore, the current paper can provide guidance to the technological research on hydrogen injectors in hydrogen internal combustion engine.

Mixture formation methods can have a significant impact on the performance and reliability of homogeneous charge compression ignition (HCCI) engines fueled by hydrogen. This paper investigates the ability of fuel injection strategies based on multiple-pulse direct injection (DI) as well as combinations of port fuel injection (PFI) and direct injection to prepare an ideal in-cylinder hydrogen–air mixture and control the autoignition process. Computations are performed using the one-dimensional turbulence (ODT) model formulated for engine simulations. It is found that multiple DI and hybrid PFI/DI schemes can be used for varying load requirements that could lead to an extension of the operating range of HCCI engines. A combination of volumetric autoignition and localized high-temperature burning are found to occur.