Exhaust Gas Recirculation

Stringent emission regulations combined with customer demands for improved fuel economy and performance have forced the automotive industry to consider more advanced powertrain configurations than standard port-fuel injected gasoline engines. Modern state-of-the-art powertrain systems may combine several power sources (internal combustion engines, electric motors, fuel cells, etc.) and various exhaust aftertreatment devices (catalytic converters, lean NOx traps, particulate filters, etc.) in addition to conventional engine subsystems such as turbochargers and exhaust gas recirculation. The determination of the way in which these systems need to be operated to meet driver's torque demand, performance and fuel economy expectations while satisfying federal emission regulations is a complex and a multiobjective optimal control problem. This paper reviews some of the approaches to this problem in the context of two case studies

Experimental study has been carried out to investigate performance parameters, emissions, cylinder pressure, exhaust gas temperature (Texhaust) and engine wall temperatures (Twall) for direct injection diesel engine. Tests were conducted for sunflower oil (S100) and 20% jojoba oil+80% pure diesel fuel (B20) in comparison to pure diesel fuel with different engine speeds. S100 and B20 were selected for the study

Ammonia and hydrogen can be produced from water, air and excess renewable electricity (Power-to-fuel) and are therefore a promising alternative in the transition from fossil fuel energy to cleaner energy sources. An Homogeneous-Charge Compression-Ignition (HCCI) engine is therefore being studied to use both fuels under a variable blending ratio for Combined Heat and Power (CHP) production. Due to the high auto-ignition resistance of ammonia, hydrogen is required to promote and stabilize the HCCI combustion. Therefore the research objective is to investigate the HCCI combustion of varying hydrogen-ammonia blending ratios in a 16:1 compression ratio engine. A specific focus is put on maximizing the ammonia proportion as well as minimizing the NOx emissions that could arise from the nitrogen contained in the ammonia. A single-cylinder, constant speed, HCCI engine has been used with an intake pressure varied from 1 to 1.5 bar and with intake temperatures ranging from 428 to 473 K. Stable combustion was achieved with up to 70 %vol. ammonia proportion by increasing the intake pressure to 1.5 bar, the intake temperature to 473 K, and the equivalence ratio to 0.28. From pure hydrogen to 60 %vol. ammonia proportion, the combustion efficiency only lost 0.6 points. Pure hydrogen Indicated Mean Effective Pressure (IMEP) was limited to 2.7 bar to avoid ringing (i.e. too high pressure rise rate) but blended with ammonia the IMEP safely reached 3.1 bar. For pure hydrogen, NOx emissions were below 6 ppm. For hydrogen-ammonia blends, NOx were between 750 and 2000 ppm. Exhaust Gas Recirculation (EGR) operations significantly reduced NOx emissions through a reduced oxygen availability but with a noticeable negative effect on combustion efficiency due to lower in-cylinder temperatures. Moreover, performed simulations showed the production of significant N2O quantities for combustion temperatures under 1400 K. Ammonia showed to be an effective fuel for HCCI conditions and EGR revealed itself as a promising NOx reducing technique through a decreased oxygen availability. Still, further effort is required when using EGR to keep the combustion temperature above 1400 K to maintain good combustion efficiencies and avoid N2O production.

The major focus of this research is to analyze the individual parameters, such as, fuel chemistry, EGR, intake air temperature and engine speed that affect the HCCI combustion on-set and to utilize in-cylinder reformation as means of controlling the HCCI combustion ...

In this study, the performance and emissions characteristics of diesel engine with four cylinders, four strokes, liquid
cooling, turbocharger and direct injection operating on 20% soybean methyl ester (SME) and 80% diesel fuel blend as
volume was theoretically investigated with different EGR ratios by utilizing the simulation software Diesel-RK. EGR
ratios of 0%, 5%, 10%, 15% and 20% were used. As performance outputs of the study, engine power and specific fuel
consumption (BSFC) changing with engine speed and in cylinder pressure and temperature changing with crank angle
at maximum torque speed and maximum power speed were presented. As exhaust emission characteristic values, NOx,
PM and carbon dioxide (CO2) emissions changing with engine speed were provided. NOx emissions were reduced at a
range of 16%-74%, PM emissions were increased at a range of 22%-154% and power output values were decreased at a
range of 11%-38% with increased EGR rates. For the SME and diesel blend, EGR ratio of 10% strategy were found to
be favorable in terms of NO
x and engine performance.

This study investigates the effect of exhaust gas recirculation (EGR) on the cycle-to-cycle variations (CCV) in combustion in a natural gas spark ignition engine. The engine is operated at 2000 rpm and a stoichiometric fuel-air mixture is used. The EGR level is changed from 0% to 5%, 10%, 15%, and 20%. For each EGR level, a continuous wavelet transform is used to analyze the time series of the indicated mean effective pressure (IMEP) over 200 cycles. The dominant oscillatory modes of the CCV are identified and the engine cycles over which these modes may persist are delineated. The results reveal that the CCV of the IMEP occur on multiple timescales and exhibit complex dynamics. With no EGR, mainly high frequency intermittent fluctuations are observed. As the EGR level is increased, more persistent low frequency variations tend to develop. In addition, the spectral power increased with an increase in the EGR level. At the EGR level of 20%, the spectral power is found to increase significantly indicating that EGR has a pronounced effect on increasing the CCV. Knowledge of the dominant modes of variability may be useful to develop effective control strategies for reducing the CCV and improving engine performance in the presence of EGR.► A natural gas SI engine with exhaust gas recirculation (EGR) is examined. ► Cyclic variability of indicated mean effective pressure (IMEP) is studied. ► The IMEP time series are analyzed using a continuous wavelet transform. ► The results show the dominant modes of variability. ► The results also reveal that EGR increases the cyclic variability of IMEP.

In internal combustion engines, instantaneous exhaust pressure measurements are difficult to perform in a production environment. The high temperature of the exhaust manifold and its pulsating character make its application to exhaust gas recirculation control algorithms impossible. In this paper an alternative method for estimating the exhaust pressure pulsation is presented. A numerical model is built which enables the exhaust pressure pulses to be predicted from instantaneous turbocharger speed measurements. Although the model is data based, a theoretical description of the process is also provided. This combined approach makes it possible to export the model for different engine operating points. Also, compressor contribution in the turbocharger speed pulsation is discussed extensively. The compressor contribution is initially neglected, and effects of this simplified approach are analysed.