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Currently, diesel engines are more preferred over gasoline engines due to their higher torque output and fuel economy. However, diesel engines confront major challenge of meeting the future stringent emission norms (especially soot particle emissions) while maintaining the same fuel economy. In this study, nanosize range soot particle emission characteristics of a stationary (non-road) diesel engine have been experimentally investigated. Experiments are conducted at a constant speed of 1500 rpm for three compression ratios and nozzle opening pressures at different engine loads. In-cylinder pressure history for 2000 consecutive engine cycles is recorded and averaged data is used for analysis of combustion characteristics. An electrical mobility-based fast particle sizer is used for analyzing particle size and mass distributions of engine exhaust particles at different test conditions. Soot particle distribution from 5 to 1000 nm was recorded. Results show that total particle concentration decreases with an increase in engine operating loads. Moreover, the addition of butanol in the diesel fuel leads to the reduction in soot particle concentration. Regression analysis was also conducted to derive a correlation between combustion parameters and particle number emissions for different compression ratios. Regression analysis shows a strong correlation between cylinder pressure-based combustion parameters and particle number emission.

Homogenous charge compression ignition (HCCI) combustion can significantly reduce automotive pollution and increase the thermal efficiency of the engine. However, combustion phasing control is a major challenge in HCCI engines due to severe cyclic combustion variations. This study investigates the cyclic combustion dynamics of the HCCI engine using nonlinear dynamic methods such as return maps, recurrence plots (RPs), and recurrence quantitative analysis (RQA). Combustion stability and cyclic variations of HCCI combustion parameters were investigated on a modified four-stroke diesel engine. The experiments were conducted by varying relative air-fuel ratios (λ) and intake air temperatures ( T i ) at two engine speeds. In-cylinder pressure data of 2000 consecutive engine combustion cycles is logged for each test condition. In this study, deterministic characteristics of combustion phasing (CA50) and crank angle position of maximum cylinder pressure ( θ P max ) are investigated and compared by employing nonlinear dynamical methods. Return maps revealed that θ P max is having distinct and more frequently observed deterministic characteristics in comparison to CA50. Patterns in RPs showed a more persistent and sudden change in the combustion dynamics at higher engine speeds. Recurrence plot-based analysis found the existence of deterministic features in the combustion dynamics irrespective of the operating conditions. It was found using RQA parameters that the deterministic nature becomes stronger with a decrease in T i and any deviation in intermediate values of λ. Additionally, RQA measures advocate that CA50 has more deterministic characteristics at higher engine speed while θ P max at lower engine speed. Strong coupling and synchronization between θ P max and CA50 is indicated by cross-recurrence plots and CPR index when engine operated with a comparatively richer mixture. [ABSTRACT FROM AUTHOR]

A noisy nonlinear dynamical (NND) model available for cyclic variations in SI engines is examined using nonlinear time series methods. Heat release time series computed from this model is analyzed by employing bifurcation diagrams, return maps, recurrence plots, and recurrence quantitative analysis techniques. The analysis methodology is at first applied to a noisy Logistic map to optimize the necessary parameters, and later the same is used for the NND map. The presence of noise hides the local patterns of the dynamics and higher periodic orbits, making the bifurcation diagrams look fuzzy for both maps. An increase in the noise level and uncombusted residuals in the NND map advance the onset point of bifurcations toward a higher equivalence ratio. The application of the NND model is extended to represent the SI engine combustion dynamics for a higher amount of internal EGR as it is favored for cycle-resolved control due to its feedback period of one combustion cycle. The combined effect of lean charge and internal EGR leads to a more complex dynamical nature. The addition of a higher amount of internal EGR adds some complex chaotic-like regions in the bifurcation diagrams. For a low level of fluctuations in the NND map, more than four noisy periodic orbits are observed for such operating conditions. The geometry of phase space trajectories for the low-level noisy model data with a high level of internal EGR resembles a chaotic system. Bifurcation diagrams, recurrence plots, and quantitative recurrence analysis indicate an intermittent route to chaos at a highly lean and diluted charge. The presence of deterministic chaotic characteristics in combustion dynamics, along with effort-saving techniques of data acquisition and estimating combustion phasing, depicts the possibilities of practical application in active onboard control of engine systems. [ABSTRACT FROM AUTHOR]

This work investigates the influence of fuel injection events on the nanoparticle emission characteristics of light-duty gasoline-diesel RCCI engine. The formation of nanoparticle emissions strongly depends on fuel injection events. The present study experimentally investigates the influence of diesel injection pressure, injection timing, and port-injected gasoline mass on the nanoparticles emitted from the gasoline-diesel RCCI engine. For this purpose, the engine is tested at different engine speeds and a fixed load of 1.5 bar BMEP without exhaust gas recirculation. The particle-size and number distribution (PSD) and total particle number (total PN) concentration are measured using a differential mobility spectrometer. The results depict that at higher diesel injection pressure (IP) operation, the peak of the NMP increases while the AMP peak decreases for neat diesel operation as well as RCCI engine. Nucleation, as well as accumulation mode particles, increases with advanced diesel injection timing in RCCI combustion. An increase in port fuel injected mass also leads to an increase in the total particle concentration and total unburned hydrocarbon (THC) emissions. [ABSTRACT FROM AUTHOR]

In present study, the effect of fuel premixing ratio, direct fuel injection timings and engine compression ratio on the soot particle emissions in nano-size range from a non-road compression ignition engine is investigated. Experiments are conducted on modified dual fuel single cylinder engine at 1500 rpm. To run the engine in dual fuel mode, port fuel injection (PFI) system is installed by modifying intake manifold of the engine and developing a PFI controller. Experiments are conducted for various fuel premixing ratio of gasoline/methanol-diesel at different engine load, diesel fuel injection timing and compression ratios. Differential mobility spectrometer based particle sizer is used for investigation of the soot particle number-size distribution, surface area-size distribution, particle mass-size distribution and total particle number concentration from the engine exhaust at various test conditions. Results revealed that total particle number concentration is higher at full engine load and increases with fuel premixing ratio (especially in case of methanol-diesel dual fuel operation). Additionally, the peak particle number and mass concentration reduces with an increase in compression ratio of the engine. [ABSTRACT FROM AUTHOR]

Alcohols (ethanol and methanol) are being widely considered as alternative fuels for automotive applications. At the same time, homogeneous charge compression ignition (HCCI) engine has attracted global attention due to its potential of providing high engine efficiency and ultralow exhaust emissions. Environmental legislation is becoming increasingly stringent, sharply focusing on particulate matter (PM) emissions. Recent emission norms consider limiting PM number concentrations in addition to PM mass. Therefore, present study is conducted to experimentally investigate the effects of engine operating parameters on the PM size-number distribution in a HCCI engine fueled with gasoline, ethanol, and methanol. The experiments were conducted on a modified four-cylinder diesel engine, with one cylinder modified to operate in HCCI mode. Port fuel injection was used for preparing homogeneous charge in the HCCI cylinder. Intake air preheating was used to enable auto-ignition of fuel-air mixture. Engine exhaust particle sizer (EEPS) was used for measuring size-number distribution of soot particles emitted by the HCCI engine cylinder under varying engine operating conditions. Experiments were conducted at 1200 and 2400 rpm by varying intake air temperature and air-fuel ratio for gasoline, ethanol, and methanol. In this paper, the effect of engine operating parameters on PM size-number distribution, count mean diameter (CMD), and total PM numbers is investigated. The experimental data show that the PM number emissions from gasoline, ethanol, and methanol in HCCI cannot be neglected and particle numbers increase for relatively richer mixtures and higher intake air temperatures. [ABSTRACT FROM AUTHOR]

Highlights: [•] Combustion phasing is analyzed by fitting probability density functions. [•] Combustion stability improves on increasing intake air temperature. [•] Test conditions with late start of combustion have larger cyclic variations. [•] Large deviations from normal distribution in combustion duration for knocking/misfire. [•] GEV distribution covers full range of distribution shapes for combustion duration/phasing. [Copyright &y& Elsevier]

Abstract: Combustion instability and cyclic variations lead to the requirement of closed loop control for use of homogeneous charge compression ignition (HCCI) engine technology for automotive applications. The closed loop control of HCCI combustion requires robust combustion timing parameters with a systematic and detailed study of its variations vis-à-vis engine operating conditions. An experimental study is conducted to provide insight into cyclic variations of HCCI combustion phasing for two fuels (gasoline and methanol) using statistical techniques. In this study, cycle-to-cycle variations of heat release parameters such as Maximum Rate of Heat Release (ROHRmax), 10% Mass Burn Fraction (MBF), 50% MBF, 90% MBF and Indicated Mean Effective Pressure (IMEP) of HCCI combustion engine fueled with methanol and gasoline were investigated using a modified two-cylinder, four-stroke engine. The experiments were conducted with different engine operating conditions at constant intake air temperature (140°C) and different air–fuel ratios at constant engine speed (1500rpm). To evaluate the cycle-to-cycle variations of combustion parameters at different test conditions, coefficient of variation (COV) and standard deviation of parameters were used. The results showed that CA50 (crank angle position of 50% MBF) is a robust parameter for the closed loop control of HCCI combustion. [Copyright &y& Elsevier]

• Presents effect of diesel SOI and PFI mass on the particle and unregulated emissions. • SOI timing, PMR, and α show a good correlation with particle number concentration. • Depicts parameters useful for prediction, control, and model development for particles. • Advanced SOI timing and increase in 'm g ' lead to increase the peak of NMP and AMP. nucleation and accumulation mode particles. • Unsaturated hydrocarbons emission increases with advanced diesel SOI timings. The study aims to experimentally characterize the nano-particle emissions and un-regulated (i.e., saturated and unsaturated hydrocarbons and formaldehyde emissions) emissions. Present study experimentally investigates the effect of high reactivity fuel injection timings and port-injected-fuel mass on nano-particle and unregulated emissions in the gasoline-diesel RCCI engine. Additionally, empirical correlations are developed using experimental data for the estimation of particle emission characteristics. An automotive single cylinder diesel engine is modified for an in-cylinder blending of port-injection of gasoline during suction stroke and direct-injection of diesel fuel during the compression stroke. The experiments are performed on a modified engine for various diesel injection timings and port-injected gasoline mass using development electronic control unit (ECU). Nano-particle and unregulated emissions are measured using electrical mobility based particle-sizer and Fourier-transform infrared spectroscopy analyser respectively. Combustion analysis is performed by in-cylinder pressure measurement. The experimental data of nano-particle and combustion characteristics are used for the development of empirical correlation using a multivariable regression technique for determining the particle number characteristics. The parameters - premixing ratio, start of injection of diesel, and a novel parameter defined as premixed fraction of total heat release are used for the development of empirical correlations and found a good correlation for estimating the nano-particle emission characteristics. Results also indicate that advanced direct injection timing and increase in the port-injected gasoline mass leads to higher particle emissions as well as saturated, unsaturated hydrocarbon and formaldehyde emissions. [ABSTRACT FROM AUTHOR]