Search

Traffic vehicles, many of which are powered by port fuel injection (PFI) engines, are major sources of particulate matter in the urban atmosphere. We studied particles from the emission of a commercial PFI-engine vehicle when it was running under the states of cold start, hot start, hot stabilized running, idle and acceleration, using a transmission electron microscope and an energy-dispersive X-ray detector. Results showed that the particles were mainly composed of organic, soot, and Ca-rich particles, with a small amount of S-rich and metal-containing particles, and displayed a unimodal size distribution with the peak at 600 nm. The emissions were highest under the cold start running state, followed by the hot start, hot stabilized, acceleration, and idle running states. Organic particles under the hot start and hot stabilized running states were higher than those of other running states. Soot particles were highest under the cold start running state. Under the idle running state, the relative number fraction of Ca-rich particles was high although their absolute number was low. These results indicate that PFI-engine vehicles emit substantial primary particles, which favor the formation of secondary aerosols via providing reaction sites and reaction catalysts, as well as supplying soot, organic, mineral and metal particles in the size range of the accumulation mode. In addition, the contents of Ca, P, and Zn in organic particles may serve as fingerprints for source apportionment of particles from PFI-engine vehicles.

An investigation of hydrocarbon (HC) and aldehyde emissions from the combustion of 2-methylfuran (MF) was conducted, with samples taken from the exhaust of a single cylinder direct-injection spark ignition (SI) research engine. This article validates the mechanism of MF combustion, and assesses its toxic emissions. Aldehyde emissions from MF were quantitatively measured using high performance liquid chromatography, and the results were compared with those of gasoline, 2,5-dimethylfuran (DMF), ethanol, methanol, and n-butanol. The detected aldehydes were mainly formaldehyde and acetaldehyde. Reaction pathway analyses of the combustion of MF and DMF were performed using a closed homogeneous constant volume reactor model in the Chemkin package. The formaldehyde emission was related to the side chain of MF. It was only half that of DMF and it was much lower than those of other fuels. The acetaldehyde emission from MF was also one of the lowest among all tested fuels. HCs from MF combustion were qualit...

This paper reports the experimental and numerical results of soot formation in laminar coflow diffusion flames of vaporized gasoline/ethanol blends at atmospheric pressure to gain improved understanding of ethanol addition to gasoline on soot formation. Four gasoline/ethanol blends of different ethanol mole fractions in the fuel stream ranging from 0% up to 85%, E0, E20, E50, and E85, were investigated to quantify how soot loading varies with the amount of ethanol blending in the fuel. The laminar coflow diffusion flames were generated using a burner system designed for vaporized liquid fuels. The fuel stream was heavily diluted with nitrogen to lower the boiling points and to prevent the flames from smoking. The soot volume fraction distributions were measured using a 2D line-of-sight attenuation technique. These flames were also modeled numerically using the extensively validated CoFlame code and a recently developed reaction mechanism for gasoline surrogates including PAH formation. The results of experiment and numerical modeling agree quite well in terms of the levels of soot volume fraction and they both show a decrease in the soot loading as more ethanol is added in the fuel stream. The measured peak soot volume fraction occurs in the flame centerline region. The soot model used in this study is unable to capture this experimental feature and predicts the peak soot volume fraction in the co-annular region. Ethanol addition reduces the soot loading primarily by lowering soot inception and PAH condensation rates through decreasing the concentrations of aromatics. Additional measurements in gasoline surrogate/ethanol blend flames indicate that the gasoline surrogate model emulates well the sooting propensity of the real gasoline fuel.

A study to extend the low load limit of the mixture of commercial gasoline and diesel in the compression mode is performed on a single cylinder diesel engine. The additional measures, like intake heating, rebreathing, negative valve overlap, are not employed. By adopting boosting, sweeping the injection pressure and varying the fuel octane number, the minimum fuelling rate and the minimum IMEP gained is compared. Besides, the thermal efficiency and emission results at these operation points are also discussed. The results illustrate that the high intake pressure, the low injection pressure and the low fuel octane number are very effective to extend low load limit. With these strategies, gasoline-type fuels can get the lowest load 0.07 MPa IMEP (0.14 MPa intake pressure and 20 MPa injection pressure) and successfully replace diesel at low load operation points in the compression mode. Increasing the intake pressure and reducing the injection pressure can significantly reduce the minimum fuelling rate and then the minimum IMEP. The minimum IMEP (0.34 MPa) of the calibration point on the original engine at test speed (1600 rpm) can be achieved by G80 without boosting. The combustion efficiency is influenced by the intake pressure and the injection pressure, however, the ISFC is more dependent on the engine load rather than other factors. If there is more over-lean mixture in cylinder when adjusting the experimental conditions, CO and HC emissions are higher. To satisfy the Euro VI regulation on NOx (

Polyoxymethylene dimethyl ethers (PODEn) have high oxygen content, cetane number and solubility in diesel fuel. In this work, pure diesel and PODE 3-4 /diesel blends with 10-20% PODE 3-4 by volume were tested in a light-duty (LD)direct injection diesel engine without any modifications on the engine fuel supply system. Engine performance, combustion and emission characteristics were compared at various loads. The results show that PODE 3-4 /diesel blends improve engine efficiency and reduce engine-out emissions significantly, especially soot emissions. The ESC test cycle in a six-cylinder heavy-duty (HD) production diesel engine fuelled with pure diesel and 20% PODE 3-4 was also conducted and similar results were achieved. It is proved that PODE 3-4 , of which the mass production has been achieved recently, is a promising blending component for diesel fuel.

An advanced combustion strategy namely “multiple premixed compression ignition” (MPCI) can exploit multiple combustion regimes. In this paper, the two-stage premixed combustion (i.e. low-temperature combustion and high-temperature combustion) using relatively low-reactivity and high volatility fuel is uncovered in MPCI mode. The mixture formation and combustion processes of low-octane gasoline MPCI mode is resolved by KIVA–CHEMKIN. The low-octane gasoline (G70H30) modeled in this study is a mixture of 70% gasoline and 30% n-heptane by volume, and it is represented by iso-octane and n-heptane oxidation mechanism. A discrete multi-component (DMC) vaporization model is used to simulate the evaporation process of G70H30, while a simplified 12-step GRI-Mech model and a two-step soot model are applied for the NOx and soot calculation, respectively. As a comparative study, partially premixed compression ignition (PPCI) mode of G70H30 is also simulated using the same numerical models. From the longitudinal and transverse sections of the combustion chamber, temporally and spatially distributed combustion events are found in the MPCI mode. That is to say, the first low temperature premixed compression ignition occurs outside of the piston bowl, and it occurs mainly in the squeeze zone above the piston triggered by the local fuel rich region. Then the second high temperature premixed combustion, which is controlled by the local turbulence resulting from the second fuel injection and chamber wall interaction, is located in the center of the combustion chamber. The temporally and spatially distributed combustion in MPCI mode decreases the local temperature, resulting in less NOx formation and lower heat transfer losses. However, there is no marked combustion distribution phenomenon in the G70H30 PPCI mode, and more NOx is generated due to higher local temperature. In addition, the early first injection of MPCI and PPCI causes spray-liner impingement, and becomes the main source of soot formation in the subsequent combustion processes.

This article describes a novel experimental method to visualize the mode shapes of pressure oscillation in a cylindrical cavity. Acoustic resonance in a cavity is a grand old problem that has been under investigation (using both analytical and numerical methods) for more than a century. In this article, a novel method based on high speed imaging of combustion chemiluminescence was presented to visualize the mode shapes of pressure oscillation in a cylindrical cavity. By generating high-temperature combustion gases and strong pressure waves simultaneously in a cylindrical cavity, the pressure oscillation can be inferred due to the chemiluminescence emissions of the combustion products. The mode shapes can then be visualized by reconstructing the images based on the amplitudes of the luminosity spectrum at the corresponding resonant frequencies. Up to 11 resonant mode shapes were clearly visualized, each matching very well with the analytical solutions.

This study investigated the filtration and continuous regeneration of a particulate filter system on an engine test bench, consisting of a diesel oxidation catalyst (DOC) and a catalyzed diesel particulate filter (CDPF). Both the DOC and the CDPF led to a high conversion of NO to NO2 for continuous regeneration. The filtration efficiency on solid particle number (SPN) was close to 100%. The post-CDPF particles were mainly in accumulation mode. The downstream SPN was sensitively influenced by the variation of the soot loading. This phenomenon provides a method for determining the balance point temperature by measuring the trend of SPN concentration.

This paper investigates the effect of naphtha (RON = 65.6) and commercial gasoline (RON = 94.0) on Multiple Premixed Compression Ignition (MPCI) mode. The experiment is conducted on a single cylinder research diesel engine with compression ratio of 16.7. The engine is operated at an engine speed of 1600 rpm for the IMEP from 0.4 to 1.4 MPa. Commercial diesel (CN = 56.5) is also tested in Conventional Diesel Combustion (CDC) mode as a baseline. At each operating point, the injection strategy and intake conditions are adjusted to meet with the criteria (NOx

Gasoline vehicles greatly contribute importantly to urban particulate matter (PM) pollution. Gasoline direct injection (GDI) engines, known as their higher fuel efficiency than that of port fuel injection (PFI) engines, have been increasingly employed in new gasoline vehicles. However, the impact of this trend on air quality is still poorly understood. Here, we investigated both primary emissions and secondary organic aerosol (SOA) formation from GDI and PFI vehicles under urban-like condition, using combined approaches involving chassis dynamometer measurement and environmental chamber simulation. The PFI vehicle emits slightly more volatile organic compounds, e.g., benzene and toluene, whereas the GDI vehicle emits more particulate components, e.g., the total PM, elemental carbon, primary organic aerosols and polycyclic aromatic hydrocarbons. Strikingly, a much higher SOA production (by a factor of approximately 2.7) is found from the exhaust of the GDI vehicle than that of the PFI vehicle under the same conditions. More importantly, the higher SOA production found in the GDI vehicle exhaust occurs concurrently with lower concentrations of traditional SOA precursors, e.g., benzene and toluene, indicating a greater contribution of intermediate volatility organic compounds and semivolatile organic compounds in the GDI vehicle exhaust to the SOA formation. Our results highlight the considerable potential contribution of GDI vehicles to urban air pollution in the future.

Gasoline vehicle exhaust is an important contributor to secondary organic aerosol (SOA) formation in urban atmosphere. Fuel composition has considerable potential impact on gasoline SOA production, but this impact is still taken little account in the emission regulations due to the poor understanding of the link between fuel components and SOA production. Here, we present an in-depth study to investigate the impact of gasoline aromatic content on SOA production through chamber approach. A significant amplification factor of 3–6 for SOA productions from gasoline exhausts was observed as gasoline aromatic content rose from 29 % to 37 %. Considerably higher emissions of aromatic volatile organic compounds performed an essential role in the SOA production enhancement. Our findings indicate that gasoline aromatics have significant influence on ambient PM2.5 concentration in megacities and highlight that more stringent regulation on gasoline aromatic content will achieve unexpected benefit on air quality in urban areas.

In previous studies, multiple premixed compression ignition (MPCI) has been proposed as a novel combustion concept in gasoline compression ignition engines which has great potential to achieve high thermal efficiency and low emissions simultaneously. MPCI mode was realized by a sequence of “spray–combustion–spray–combustion” around the compression top dead center (TDC). This study is aimed for the high load expansion of naphtha MPCI. In addition, the study investigated advantages and disadvantages of MPCI compared with partially premixed compression ignition (PPCI) and conventional diesel combustion (CDC). Engine operating range successfully reached indicated mean effective pressure (IMEP) of 1.4 MPa with high thermal efficiency, low emissions and acceptable combustion noise by the optimization of the injection parameters and the intake management. For MPCI, earlier combustion phasing was possible even at the high load operation compared with PPCI and CDC. This was attributed to the separated heat release characteristics and pressure rise rate process. The divided pressure rise rate process caused considerably low maximum pressure rise rate (MPRR) characteristics such as 0.8 MPa/deg at IMEP 1.4 MPa condition. The earlier combustion phasing led to the higher thermal efficiency characteristics of MPCI combustion compared with PPCI and CDC. This was attributed to the lower exhaust heat loss characteristics. However, high level of hydrocarbon (HC) and carbon monoxide (CO) emissions with low combustion stability at the low load operation were considered as severe challenges to overcome.

Experimental and numerical studies have been performed on the thermal and chemical effects of buffer gas composition on low temperature ignition of iso-octane and n-heptane. Experiments were conducted using a recently developed rapid compression machine in the temperature range of 600–850 K. Three buffer gases were studied including nitrogen (N 2 ), argon (Ar), and a mixture of Ar and carbon dioxide (CO 2 ) at a mole ratio of 65.1%/34.9%. Iso-octane was studied at 20 bar, ϕ = 1, and a dilution level of buffer gas to O 2 of 3.76:1 (mole ratio). n-Heptane was studied at 9 bar, ϕ = 1, and a dilution level of buffer gas to O 2 of 5.63:1 (mole ratio). For experiments where two-stage ignition was observed, the buffer gas composition had no impact on the first-stage ignition time but, as expected, it caused differences in the total heat release, pressure and temperature rise after the first-stage ignition. As a consequence, significant differences were observed for the total ignition delay time as a function of the buffer gas composition, with up to 40% and 42.5% faster total ignition time for iso-octane and n-heptane, respectively, by using Ar instead of N 2 . The chemical effects of the buffer gas composition were studied experimentally by comparing the results of the N 2 and Ar/CO 2 (65.1%/34.9%) mixtures, recognizing that while the Ar/CO 2 mixture has the same heat capacity as N 2 , its predicted combined third-body collision efficiency is about 76% higher than N 2 . The experimental results showed negligible chemical effects on the first-stage and total ignition delay times. Numerical simulations were carried out over a wider range of temperatures for pure N 2 , Ar, and CO 2 as buffer gases. Results showed that thermal effects are very pronounced and dominated at the negative temperature coefficient and two-stage ignition conditions, which is consistent with the experimental results and previous studies in the literature. However, the simulation results also showed at temperatures higher than 850 K, the chemical effects of CO 2 became more important than the thermal effects.

The non-volatile particle emission characteristics of alternative (rapeseed methyl ester and gas-to-liquid) diesel fuel blends were studied through an experimental investigation carried out on a light-duty common-rail diesel engine. A blend ratio of 10 vol % was chosen as the practical limit for biodiesels in this study, and the research focus was on the particle number concentration and size distribution with various injection strategies, in which the non-volatile emissions were measured using thermodilution. The particle morphology and mass, together with the related gaseous emissions, were measured and analysed. The results indicate that, without any engine modification, adding selected alternative fuels even at a low percentage could result in a favourable reduction in the number of particles and in a significant reduction in the total particle concentration in both the nucleation mode and the accumulation mode. The particle emissions of the three fuels demonstrated monomodal size distributions under most engine conditions tested, except for the engine idling case, which produced a bimodal size distribution. The influence of 10 vol % rapeseed methyl ester or gas-to-liquid diesel blends on the carbon monoxide and nitrogen oxide emissions is not significant. Nevertheless, using these diesel fuel blends may increase the total hydrocarbon emissions and may lead to high particulate matter emissions.

The furan series of chemicals such as 2,5-dimethylfuran (DMF) and 2-methylfuran (MF) are promising alternative fuel candidates for internal combustion engines due to their advantages compared to gasoline. However, no research has been published on the optical diagnostics of their combustion process in the engine cylinder. In this paper, the planar laser-induced fluorescence (PLIF) technique has been used to investigate the OH distribution in the flames of DMF and MF in a direct injection spark ignition (DISI) optical engine. The images of OH-LIF in the combustion process combined with the high-speed imaging and heat release data at two different engine load conditions (4.5 bar and 5.5 bar IMEP) for DMF and MF were studied and compared with isooctane, the reference fuel representing gasoline. Interesting correlations were found between the heat release rate, flame speed, flame area and PLIF of OH for the tested fuels at the two loads and the proposed correlations have also been confirmed by using the data in previous studies. MF is shown to combust significantly faster than DMF and isooctane. It is found that at 4.5 bar IMEP, the pressure trace, flame speed and flame area growth rate of DMF are very close to those of isooctane, but lower than those of MF. The combustion phase of MF is earlier and the duration is shorter than DMF and isooctane. Normalized LIF signals show that MF always has the maximum values and the higher IMEP will advance the time of the OH peak. The rate of heat release (ROHR) matches the trend of OH development well before the flame goes beyond the visible area. Finally, a correlation between the results of MFB and OH-LIF reveals that the three fuels follow a similar trend, indicating that the OH generation matches the MFB data well, irrespective of the fuel. The correlations between the flame area and OH-LIF signal are also discussed.

High boost and direct injection are the main tendency of gasoline engine technology. However, pre-ignition/super-knock tends to occur at low-speed high-load conditions, which is the main obstacle for improving power density and fuel economy. This work distinguished the relationship between super-knock and pre-ignition by experimental investigation and numerical simulation. The experiment was conducted on a turbocharged gasoline direct injection engine with compression ratio of 10. The engine was operated at an engine speed of 1750 r/min and the brake mean effective pressure of 2.0 MPa under stoichiometric conditions. Super-knock is the severe engine knock triggered by pre-ignition. Pre-ignition may lead to super-knock, heavy-knock, slight-knock, and non-knock. Significantly advancing spark timing can only simulate pre-ignition, not super-knock. Although knock intensity tends to increase with earlier pre-ignition timing, higher unburned mixture fraction at start of knock, and higher temperature and pressure of the unburned mixture at start of knock, knock intensity cannot be simply correlated to any of the parameters above. A one-dimensional model is set up to numerically simulate the possible combustion process of the end-gas after pre-ignition. Two distinct end-gas combustion modes are identified depending on the pressure and temperature of the mixture: deflagration and detonation. Hot-spot in the mixture at typical near top dead center pressure and temperature condition can only induce deflagration. Hot-spot in the unburned end-gas mixture at temperature and pressure conditions above ’’deto-curve’’ may induce detonation. The mechanism of deto-knock may be described as hot-spot-triggered pre-ignition followed by hotspot- induced deflagration to detonation.

This paper studies the combustion and emission characteristics of three kinds of low octane fuels which are naphtha, the blend of gasoline and diesel (G70D30), the blend of gasoline and n-heptane (G70H30) in multiple premixed compression ignition (MPCI) mode. Commercial diesel is also tested in conventional diesel combustion mode as a reference. The study is carried out in a single cylinder diesel engine with a compression ratio of 16.7. By varying the common rail pressure, the effect of injection pressure on combustion and emissions is investigated. The results illustrate that the combustion delay of the gasoline-type fuels is extended with the increase of injection pressure. The soot emission decreases at high injection pressure with a penalty of higher CO and HC emissions. Increasing the injection pressure also reduces the particle number in accumulation mode, but produces more in nucleation mode. Among the test fuels, naphtha has the lowest NO x emission due to low combustion temperature but the highest CO and HC emissions. There is no significant difference in particle size distribution for the three fuels. The indicated thermal efficiency of gasoline-type fuels increases with the rise of injection pressure and it is higher than that of diesel at high injection pressure. The diesel fuel has lower CO and HC emissions than the gasoline-type fuels, but much higher pressure rise rate, NO x and soot emissions due to high combustion temperature and poor premixing. Therefore, the low octane gasoline fuels are more suitable than the diesel for the compression ignition engines in terms of the emissions.

Stoichiometric Diesel and Gasoline Dual-fuel (Dieseline) Compression Ignition (SDCI) combustion using three-way catalyst (TWC) after-treatment is a promising technology to address the challenge issues of fuel consumption and emissions in future internal combustion engines. The authors use EGR instead of the throttle to control the load of the dual fuel compression ignition combustion engine. In order to investigate the fuel consumption and emission characteristics of SDCI combustion, a series of experiments were conducted in a modified single cylinder diesel engine using gasoline with a small portion of diesel for ignition enhancement. The experimental results show that SDCI combustion can achieve high indicated thermal efficiencies in a relatively wide range of loads (IMEP 4.3–8.0 bar) because of a higher compression ratio, shorter combustion and smaller pumping losses. An attractive indicative specific fuel consumption (ISFC) of 190.8 g/kW h has been achieved at a medium load without any boosting and the PM emissions are lower than for conventional diesel combustion. Different diesel percentages in the dual fuel supply have shown a significant impact on the ignition process and provide a wider available time range for combustion phase control. Diesel direct injection (DI) timing has a greater effect on PM emissions than the fuel ratio. Late DI timing reduces the thermal efficiency and results in higher PM emissions. Early DI timing and less diesel are preferable in order to reduce or avoid the diffusion combustion stage, which may lead to high PM emissions in the stoichiometric combustion.

Based on a detailed surface reaction mechanism of CO–O 2 reaction over rhodium, a computational fluid dynamics package coupled with CHEMKIN code was employed to analyze the flow field and catalytic reaction of full-size automotive catalytic converters. The effect of geometrical factors on flow uniformity inside a dual-substrate catalytic converter was investigated. Results indicated that with the gap width and total substrate length fixed, increasing the substrate length ratio (front substrate/rear substrate) promotes flow uniformity. The influences of substrate length ratio and precious metal loading on its light-off performance were also discussed. It was found that the converter with high substrate length ratio achieved a good flow uniformity performance, as well as possessed a low light-off temperature. The effect of precious metal loading was analyzed and a significant improvement in CO conversion was obtained at a typical low temperature for all the three substrates with different cell density when the content of precious metal loading was doubled. Furthermore, the light-off temperature of the 400 cpsi/6.5 mil substrate was lowered with increasing precious metal loading. The predicted results reveal that the coupling approach of detailed kinetic model and flow field can be a proper method in optimization of converter design.

Double injection strategies with single-stage heat release and two-stage heat release process of straight-run naphtha were investigated on a single-cylinder diesel engine from low to high load. The two-stage combustion strategy is realized by split spray and combustion events around the compression top dead center with a dominant feature of “Combust After Injection End, Inject After Combustion End” to ensure the premixed compression ignition. The single-stage combustion is realized by the “spray–spray–combustion” process with the start of combustion separated from the end of injection. The straight-run naphtha has a research octane number of 58.8, and the compression ratio and displacement of the test engine are 16.7 and 0.5 L. Double injection strategy is used to generate the single- and two-stage combustion modes with different injection timing. NOx and total hydrocarbon emissions of the two-stage combustion mode are lower than that of single heat release mode in this study, and it is much easier to produce two-stage combustion mode at higher engine load. Diesel is also tested under double injection strategy just as the single heat release mode of straight-run naphtha, but the fuel efficiency and emission performance are worse than that of naphtha.

Two-stage split-injection strategies for partially premixed compression ignition (PPCI) combustion mode were investigated in a light duty 2.2 L four cylinder compression ignition engine fuelled with G50-Dieseline (50% ULG95 gasoline in EN590 diesel by volume). The investigation of two-stage split-injection has been focused on injection quantity-ratios and timings and it aims to achieve improved charge premixing and consequently reduce the oxides of nitrogen (NO x ) and particulate matter (PM) emissions simultaneously. Other parameters affecting combustion process (e.g. compression ratio) were fixed to identify the individual effects of parameters under study on the combustion and emission characteristics by the Taguchi-DOE (design of experiment) analysis. The investigation was conducted for two load groups of 1.37 and 2.97 bar BMEP selected from the new European driving cycle (NEDC) at an engine speed of 1800 RPM. Optimum operating values of injection parameters for generating the minimum and maximum combustion and emission characteristics were identified. Furthermore, very early first injection-timings were investigated for 2.97 bar BMEP with the combustion phase of 50% accumulative heat release (AHR-50) fixed. Compared with the single-injection strategy, BSNO x was reduced by approximately 39% to 59% through applying the two-stage split-injection. Accumulation particulate concentration as well as smoke number were reduced by approximately 90%. It is believed that with very early first-injection timings, fuel wall-impingement and over mixing may have resulted in lower combustion efficiency and thus BMEP drop. Consequently, the premixing process can reach a limit where the effect of required higher injected fuel quantity dominates combustion and emission characteristics. The two-stage split-injection developed in this study appears to be effective in improving the premixing process for PPCI combustion.

To meet the needs of fuel security and combat the growing concerns of CO2 emissions, the automotive industry is seeking solutions through biofuels. Traditionally, when supplying biofuel blends to the combustion chamber, the blend is mixed externally prior to its injection in one location. This location occurs either before the cylinder (port-fuel injection, PFI), or directly into the cylinder (direct-injection, DI). However, the use of dual-injection allows the in-cylinder blending of two fuels at any blend ratio, when combining the two locations (PFI and DI). This injection strategy offers increased flexibility as the blend ratio can be changed instantaneously according to engine speed and load demand and fuel availability. Previous work by the authors has reported the improved combustion performance of dual-injection with 25% blends (in gasoline) of a new biofuel candidate: 2,5-dimethylfuran (DMF). This current investigation extends the analysis to include the gaseous emissions of various DMF blends (25%, 50% and 75%) from 3.5 bar to 8.5 bar IMEP and the particulate matter (PM) emissions of similar fraction ethanol blends at a selected condition of 5.5 bar IMEP. Compared to DI, dual-injection offers reduced CO and CO2 emissions and comparable HC emissions. The mean PM diameter is decreased and the accumulation mode particles are negligible compared to DI. However, the implication of the higher combustion pressures is an increase in NOx due to reduced charge-cooling.

This article proposes a novel combustion mode, namely “multiple premixed compression ignition” (MPCI), in gasoline direct-injection compression ignition (GDICI) regime. Its predominant feature is the multiple premixed combustion processes in a sequence of “spray–combustion–spray–combustion” around the compression top dead center. The multiple-stage premixed combustion decouples the pressure rise with the pollutant formation process. With optimization, it can lower the rate of pressure rise and emissions simultaneously while achieving high thermal efficiency. The experimental study has been carried out in a single-cylinder research engine with a compression ratio of 18.5. Gasoline with the research octane number of 66 was tested under MPCI mode with different exhaust gas recirculation rates and injection timings. Compared to the single-stage diffusion combustion mode of conventional diesel engines, the low octane gasoline MPCI mode achieves lower emissions of smoke, NO, and CO as well as greater thermal ef...

Straight-run naphtha is tested in the newly raised combustion concept, called multiple premixed compression ignition (MPCI) mode, on a single cylinder diesel engine under different speeds. The partially premixed compression ignition (PPCI) mode is also investigated for comparison. The MPCI mode proposed by the authors was realized by multiple premixed combustion processes in a sequence of “spray–combustion–spray–combustion” around the compression top dead center (TDC). The spray and combustion events are preferred to be separated completely, with a dominant feature of “Combust After Injection End, Inject After Combustion End” to ensure the multiple-stage premixed compression ignition. The PPCI mode is well known as the “spray–spray–combustion” sequence with the start of combustion (SOC) separated from the end of injection (EOI). The straight-run naphtha has a research octane number (RON) of 58.8, and the compression ratio and displacement of the test engine is 16.7 and 0.5L. Double injection strategy is employed to generate the PPCI and MPCI modes. Maximum pressure rise rate and NOx emission of the MPCI mode is lower than that of PPCI mode, and it is easier to produce MPCI mode at lower engine speed. Diesel is also tested under double injection strategy just as the PPCI mode, but the fuel efficiency and emission performance is worse than that of straight-run naphtha.

Gasoline Homogeneous Charge Induced Ignition (HCII) by diesel uses port fuel injection of gasoline to form a homogeneous charge and direct injection of diesel fuel as an ignition source. Gasoline/Diesel Blend Fuels (GDBFs) uses a premixed blend of diesel and gasoline which is directly injected into the cylinder for combustion. Exploratory studies show that these two ways may integrate the advantages of gasoline and diesel fuels to achieve high thermal efficiency and low emission targets. Combustion characteristics, emission characteristics, thermal efficiency and adaptability of low-temperature combustion in these two combustion modes have been comparatively investigated on a high-pressure common rail single-cylinder diesel engine. The results show that both HCII and GDBF modes can achieve higher thermal efficiency than gasoline SI combustion and a similar or even higher thermal efficiency than diesel CI combustion because the combustion was closer to constant volume combustion. As gasoline ratio increases, the fuel–air mixing is improved in both HCII and GDBF modes, and thus soot emissions reduced dramatically, with a biggest reduction of 90%. The ignition delay in HCII mode remained almost the same, while the ignition delay in GDBF mode increased significantly with the increase of gasoline ratio. As gasoline ratio increases, the combustion duration in both HCII and GDBF modes shortened significantly. Both HCII and GDBF modes can achieve low temperature combustion with extremely low soot and NO emissions when combined with large amounts of EGR. These modes demonstrate an advantage over the diesel CI combustion mode, where the NO emissions decreased and soot emissions increased with the increase of EGR, exhibiting the classical NO-soot trade-off.

A pilot injection has been used widely in diesel engines for the control of nitrogen oxide emissions and noise. However, very little information on the characteristics of particulate matter emissions with a pilot injection is available. In this paper, the non-volatile particle emissions of a light-duty common-rail production diesel engine under the impact of a pilot injection are studied in terms of the particle number concentration and the particle size distribution with the measurements taken with a scanning mobility particle sizer. For various key parameters such as the fuel quantity and the injection timing, the results illustrate how a pilot injection alongside a main injection could affect particulate matter emissions, which are also shown to be closely related to the engine mode and the exhaust gas recirculation level. It is revealed that advancing the pilot injection generally reduces the number and size of particles in both the accumulation mode and the nucleation mode. It is also found that an increase in the pilot fuel quantity increases the total number and size of particles, with a significant impact on the number of accumulation-mode particles, which overwhelms the decrease in the number of nucleation-mode particles.

A novel combustion concept namely “multiple premixed compression ignition” (MPCI) in gasoline direct injection compression ignition (GDICI) regime is proposed. Its predominant feature is the first premixed and followed quasipremixed combustion processes in a sequence of “spray-combustion-spray-combustion”. The multiple-stage premixed combustion decouples the pressure rise with pollutants formation process, which means the pressure rise rate and emissions can be reduced simultaneously, while achieving a high thermal efficiency. The gasoline MPCI mode has been demonstrated in a research engine with a compression ratio of 18.5. Gasoline with the research octane number (RON) of 94.4 was tested under 1400 rpm, 0.6 MPa IMEP conditions, without EGR and intake boosting. A parameter study of common rail pressure and intake temperature was implemented to investigate their effects on the performance of MPCI mode. Compared to the single-stage diffusion combustion in traditional diesel engines, the gasoline MPCI mode achieves lower emissions of soot, NO, CO, as well as slightly higher indicated efficiency, with a penalty of higher THC emissions when the common rail pressure is larger than 80 MPa in this study. With intake temperature sweeping, the gasoline MPCI mode also has the foregoing advantages compared to the diesel under the same operating conditions.