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Abstract
Lean-burn engines operate at a very lean air-to-fuel (A/F) ratio under light-load and part-load regions. Because of better combustion in the lean mixture, fuel economy enhancement is the major merit. Lean-burn technologies also give rise to high engine performance and low emission levels (hydrocarbons and carbon monoxide). In the full-load region, the engine operates in the stoichiometric or rich mode. The drawback of the lean-burn engine is its higher nitrogen oxide (NOx) emission level. The three-way catalyst acts as a suitable device near stoichiometry; however, it is inefficient when the A/F ratio is far from stoichiometry. Hence, advanced catalysts are needed to carry out the NOx storage (oxidation) and purge (reduction) operations. This article is concerned with the lean-burn control applications on gasoline engines, which can also be expanded to other types of engine. Case studies on port fuel injection (PFI) and gasoline direct-injection (GDI) engines have been conducted from different points of view. The experimental investigation on a quasi-homogeneous lean-burn PFI engine has been studied from a fuel economy and NOx reduction viewpoint. The modelling and control approaches are also presented for GDI engines to achieve ultra-lean mixtures for fuel economy enhancement and NOx emission reduction.
... Thus, to obtain same power output as that of diesel, the engine will consume additional fuel quantity when operated with Gasoline and JP-8 [4,10]. EGR also tends to increase the fuel consumption [10,22]. Gasoline and JP-8 showed about 4.4% and 3.5% higher BSFC, respectively, vis-à-vis diesel fuel. ...
... NO x emissions are produced by combustion of rich fuel mixture in presence of large quantity of oxygen [8,26]. NO x formation depends on the peak temperatures, fuel's properties and presence of oxygen in fuel [20,22]. NO x emissions for diesel were higher than Gasoline and JP-8 since it operates at higher temperatures [8]. ...
... Heat transfer is directly related to engine efficiency and emission levels, which is why a focus is given to the exhaust temperature [1]. The high dependency on the exhaust temperature for these factors is also widely recognized and a simple but accurate model is crucial for improvement [3,4]. Numerous engine, air system and injection system parameters, such as air flow, fuel injection quantity, engine speed, and rail pressure, affect the exhaust temperature [2,3]. ...
... Example of (2+4)*3 in postfix notationIn stack-based GP the three numbers(3,2,4) inFigure 3.3 are first pushed onto the empty stack and then the + instruction is executed by taking (popping) the top two numbers (2,4) from the stack. The resulting value of 6 is then pushed onto the stack and the * instruction pops the top two numbers (3,6) from the stack. ...
Genetic Programming (GP) is introduced as a symbolic regression technique
for usage in automotive modeling applications. One use case is the modeling
of the exhaust temperature in vehicles, of which two representative synthetic
functions were obtained to examine and evaluate the capabilities of Symbolic
Regression Genetic Programming.
The current state-of-the-art in GP was extensively examined and from these
findings, suitable state-of-the-art techniques are used for an implementation of
GP. The GP implementation created is then further used to conduct experi-
ments for the two synthetic problems.
The results of GP compared to well established regression methods seem
promising but also noticeably worse than for methods such as Gaussian Process
Regression. While the results are noticeably worse than the methods compared
to, GP produces an interpretable analytical function by using a quasi model-
less method, which none of the methods compared to GP do. These can also
give an insight into the general structure of the data used.
... For emission levels and converting efficiency of catalytic devices, high dependency on exhaust temperature is widely recognized. A simple but accurate exhaust temperature model is critical to exhaust emission system enhancement [4]. ...
... To implement Monte Carlo integration, statistical sampling is applied with a size S. The expectation is approximated in a way that posterior distribution is substituted by the stationary distribution π(x) of the Markov chain in steady state as (4). The model f(x) is constructed as engine exhaust temperature T Exh , which is a hybrid nonlinear function with two variables (x 1 , x 2 ) associated to engine speed and engine load, respectively. ...
Even though actual composition of engine exhaust gases varies across diverse types of engines, such as gasoline, diesel, gas turbine and natural gas engines, engine exhaust temperature is always a major factor with strong impact on emission levels and catalytic converting efficiency. For spark ignition engines, exhaust temperature depends on various engine parameters, such as engine speed, engine load, A/F ratio, intake air temperature, coolant temperature and spark timing, etc. Due to complexity, it is impossible to share a unique analytical model of engine exhaust temperature. Instead, it is mostly modeled as a complicated nonlinear system. The model complexity increases significantly however accuracy cannot be guaranteed. On the other hand, a simple linear model with accurate system identification could serve as a versatile alternative to represent the engine exhaust temperature, while engine parameters are subject to model identification to be adaptable across different types of engines. Combination of linear functions in terms of dominant engine parameters of engine speed and engine load is used for exhaust temperature modeling. To identify optimal parameters, Markov Chain Monte Carlo (MCMC) is applied. The discrete-time Markov chain is introduced where the stationary probability replaces posterior density in Monte Carlo integration for numerical integration. Compared with the high order nonlinear approaches, low computation cost is involved in the simplified model. Good agreement between the model prediction data and testing results is observed. The approach could be easily extended to other types of engines.
... 20 Lean burn also creates an increase in NO x emissions due to a reduction in three-way catalyst efficiency resulting in a lower combustion stability at high air/fuel ratios. 21 The effect of lean burn on engine efficiency was investigated on a 1.4 L GDI engine using the downsizing and turbocharging technology; the results showed that the lean mixture improved engine fuel consumption. 22 Irimescu et al. 23 studied cycle-by-cycle variations under lean operation conditions and reported the effects of operation parameters on the coefficient of variation (COV) and fuel conversion efficiency in lean mixtures. ...
Biobutanol is a promising alternative fuel for spark-ignition engines. Exhaust gas recirculation (EGR) and air dilution were evaluated on a TGDI engine fueled with butanol-gasoline (B20) in view of engine operation, efficiency, gaseous emissions, and PM emissions. For the B20 engine, EGR affected combustion more strongly than excess air dilution; the brake thermal efficiency (BTE) under excess air dilution was much higher than that with EGR. The oxygen concentration in the cylinder was also markedly reduced with EGR relative to air dilution, as the partial fresh charge was substituted with nonreactive gas. A reduced oxygen concentration contributed to differences in combustion between excess air dilution and EGR. Higher BTE was observed during combined EGR and excess air dilution operation, though it was slightly lower than that under excess air dilution alone. NO
x
was also markedly reduced by the combination of EGR and excess air dilution, but was slightly higher than that with EGR alone. Under combined dilution conditions, the particle number (PN) emissions from the B20 engine were reduced significantly, particle sizes decreased, and the nucleate PN significantly decreased.
... With the deepening of methanol research, it was found that up to 50% oxygen content was conducive to the complete combustion of fuels and then reduced the exhaust emission of hydrocarbons of vehicles. [12][13][14][15][16] And it had a great substituted ratio and its sources of raw materials were abundant, such as coal, natural gas, coke-oven gas, and coal bed methane. China has abundant coal resources, and the technology of producing methanol by coal is mature with low cost. ...
This article chose the new type alcohol-based fuel as the engine fuel, realized lean burn in a CA4GA5 engine, and got the lean burn limit to 20.6. Taking the gasoline as equivalent fuel, and according to 10%, 20%, and 30% volume proportion of alcohol-based fuel, three new types of alcohol-based gasoline synthetic fuel, M10, M20, and M30, were formed. A comparative study of the original engine emissions used new types of alcohol-based gasoline synthetic fuels with Compressed Natural Gas (CNG) and different blending ratios based on M0 at different stoichiometric air-to-fuel ratios was carried out. This article studied the influence of air-to-fuel ratio on cycle emissions under the lean burn condition and analyzed the characteristics of the new European driving cycle. Experimental results show that compared with the working condition of pure gasoline engine, the emissions of total hydrocarbon and carbon monoxide gradually reduce with the increase of alcohol-based fuel blending proportion, while the NOx content presents the rising trend.
... Very often, these types of engines run on very lean (A/F) mixtures for small and partial loads in Gasoline Direct Injection (GDi). At full loads the engine still operates at a stoichiometric mixture, yet extremely lean mixture leads to a high NO x emission [17]. Direct injected engines (GDi) contribute to an increased total emission of PM from a vehicle [18]. ...
The paper analyzes the problem of injector dosage irregularity in classical and alternative fueling systems in motor vehicles. An adoption of a newly manufactured subassembly as a starting point for the research creates idealized engine operating conditions (new engines). The question of investigating used subassemblies is rather difficult but it provides a better and clearer picture of the existing situation - the exhaust emissions. The authors have undertaken the problem of fueling irregularity as a response to a growing number of vehicles with malfunctions of LPG fueling systems that are currently very popular in Poland. In the course of the analysis, several injectors were tested to present the differences in their dosage irregularity. To realize the research tasks, different test stands with software were designed. To fully visualize the problem, several sets of injecting units were selected at different stages of their wear. The results have shown that gasoline injectors are characterized by approx 0.5% irregularity and if heavily worn - 6%. LPG vapour injectors reached the level of 5% and heavily worn ones - 50%.
Biobutanol is a promising alternative fuel, but it is accompanied by a fuel consumption penalty. To mitigate the fuel penalty, air dilution was investigated in a turbocharged gasoline direct injection engine fueled with isobutanol-gasoline (B73). To overcome issues of NOx emissions during air dilution operation, exhaust gas recirculation (EGR) and the combination of EGR and air dilution (EGR-Air) were investigated to reduce NOx emissions and enhance engine performance. The effects of these applications on particulate emissions (PM) were also assessed. Compared to EGR, there was more pronounced improvement in brake thermal efficiency (BTE) for butanol-gasoline engine under EGR-Air. The combustion stability under EGR-Air was acceptable but slightly decreased relative to that under EGR. Lower exhaust gas temperature was observed under EGR-Air with respective to EGR. EGR-Air exhibited similar effective inhibition of NOx emissions, as with EGR, which was more pronounced in reducing NOx emissions at high EGR rate, while EGR-Air reduced NOx by up to 90%. CO emissions were clearly reduced under EGR-Air conditions, which realized a better balance between BTE and NOx emissions with very low NOx concentrations. For a butanol-gasoline engine, the PM emissions under EGR-Air were further lowered compared to EGR, which showed a bimodal size distribution, and the particle sizes corresponding to the particle number peak was in the range of 10–30 nm. The observed particle diameters under EGR-Air were smaller than that with and without EGR.
The advancement of the means of transport, having its origins in the increasingly stringent exhaust emission limits, forces a better and more accurate fuel dosage to the engine. The increased computing power of the engine ECUs has led to a more precise analysis of the process. A problem arose of the adaptation of engines to LPG fueling. The uneven fuel dosage to the cylinders is partly adjusted by the injection timing. Therefore, in search for other reasons for engine inappropriate operation, the author decided to determine the cycle-by-cycle non-repeatability of fuel dosage of gas-phase injectors. To this end, an original research stand including all necessary equipment was applied. By recording the air pressure at the outlet of the nozzles of different injectors, individual cycles were analyzed. Based on the average pressure values in the cycles, the non-repeatability rate of the fuel dosage was determined. As a result of the performed research on randomly selected low-pressure gas-phase injectors, it was observed that brand new injectors have a non-repeatability rate of approx. 0.3%. For the injectors already in operation an approx. 36% non-repeatability rate was observed compared to the brand new ones. When comparing the brand new and the end-of-life (high mileage) injectors, a 1.5 times increment of the non-repeatability of the fuel dosage was determined. The determined parameter is significant because of the narrowing of the combustible mixture control window in modern engine control systems. As a result, this may lead to detecting errors when the fuel dosage repeatability is poor.
To study the effects of hydrogen direct injection strategies on the characteristics of combustion and emissions of hydrogen–gasoline engines, an experimental engine platform was built with gasoline intake injection and hydrogen direct injection. The effects of hydrogen injection pressure and injection timing at a minimum advance for the best torque on the characteristics of engine combustion and emissions were studied at a constant engine speed, air–fuel ratio, and hydrogen fraction. The test results showed that when the heat that was released in the cylinder was constant, a 10% hydrogen fraction had a significant influence on the engine's performance, combustion, and emissions. Hydrogen direct injection greatly improved the combustion stability of lean-burn mixtures of the engine, and significantly improved the mean effective pressure and thermal efficiency. Hydrogen injection at optimum ignition timing would significantly shorten the flame-development period and rapid combustion duration. The heat release was more concentrated, which increased the cylinder pressure. With an excess air ratio of 1.5, the addition of hydrogen significantly reduced CO emissions, but HC emissions increased slightly. A lean burn could contribute to the reduction of NOx emissions, whereas the addition of hydrogen would increase it.
The investigations aimed at proving the influence of selected parameters on the flow properties of LPG vapor phase injectors. The author mainly assessed the feed pressure, the injector piston lift, the diameter of the outlet nozzle and the realization of the current-modulating signal. Functional relations have been determined and qualitative assessment of the compatibility has been performed. Additionally, an evaluation of the influence of the analyzed parameters has been performed on the injector full opening and closing times that confirms the response to the impulse and may be decisive in the case of short injection times. It has been confirmed that the injector piston lift significantly influences the response times (for full opening - 1.00 ms and full closing - 1.08 ms) and the PWM duty cycle below 50% may lead to a closure of the injector due to insufficient counter force (difference for full closing by 7.53 ms at the 10 ms opening times). In order to measure the response times, an outflow meter has been proposed. A new parameter has been introduced to the analysis - opening timing that may be used in simplified flow analysis. The investigations are a response to the market demands for this type of analyses and to an increasing demand for multipoint LPG vapor phase injection systems. The investigations may turn out useful in calculations or validations of simulation models.
Excessive EGR deteriorates the NOx conversion efficiency of LNT in a lean-burn gasoline engine was found in the previous research. The numerical simulation of NOx purification under different EGR rate was conducted in a lean-burn gasoline engine with actual emission as the inlet boundary conditions. Results found that, NOx slip increases with the increase in lean-mode time and reaches the stable level before the end of the lean-mode.
An artificial neural network (ANN) model of a lean burn gasoline engine with lean-NOx trap (LNT) was built to predict the NOx emission, brake specific fuel consumption and NOx conversion efficiency of LNT. The data for training and testing the proposed ANN were obtained from a number of experiments performed with a 3-cylinder, 12-valve, electronic controlled CA3GA2 lean burn gasoline engine. A standard back propagation ANN was adopted. After the training, the performance of the ANN predictions was measured by testing data. It is found that the R2 (absolute fraction of variance) values are close to 1, and root mean squared error (RMSE) and mean relative error (MRE) values are in the acceptable range. The determination of the best lean mode period exemplifies the application of the generalization ability of ANN in the optimization and control of lean burn gasoline engine.
An adaptive model based monitoring strategy for a NOx trap catalyst is presented. First, a simplified model of the NOx trap is developed from a physical PDE (Partial Differential Equations) model. A validation on different types of data is given. Then two monitoring strategies are presented: a non-adaptive and an adaptive strategy, which uses a downstream EGO (Exhaust Gas Oxygen) sensor. The basic idea of the adaptive strategy is to put the catalyst and monitoring strategy in a particular condition such that a successive adaptation of three different parameters of the model is possible. The adaptive strategy is compared to the non-adaptive strategy by use of numerical simulations.
Gasoline direct injection (GDI) engines have superiority over port fuel injection (PFI) engines on fuel economy at the expense of extra emissions, especially NOx. In lean operations, the traditional three-way-catalyst (TWC) is no longer effective for NOx aftertreatment. As a result, lean NOx trap (LNT) is introduced for the extensive NOx aftertreatment. In homogeneous operations, the HC and CO emission control technologies in PFI engines can be potentially selected. In comparison to TWC technology, LNT technology requires a higher-level integration into the GDI powertrain systems. Its operation switches between storage mode and purge mode. Mode switching has an impact on control of emission and fuel economy as well as driveability due to the rapidly changing mass air flowrate. Its frequency adversely affects fuel economy. A trade-off exists between fuel economy and the additional aftertreatment cost. Thermal management of LNT inquires a proper temperature window to trap NOx, to avoid thermal damage and to prevent NOx desorption. In this research, LNT thermodynamics mechanism is thoroughly investigated. NOx emission control is conducted and HC and CO emission control scheme is proposed. Along with emission control, fuel economy can be improved simultaneously by taking temperature factor and oxygen storage effect into account in LNT modeling and control design. On a basis of the fuel economy and emission improvement objective, the role of the oxygen storage effect on fuel economy is analyzed and simulated. In the meanwhile, the impact of trap temperature on LNT storage time, LNT purge time and fuel economy is examined. New technologies during cold start are suggested for HC and CO reductions.
A novel catalyst converter system has been developed for NOx emission aftertreatment of lean burn gasoline engines. The goal is to investigate its impact on emission characteristic and Break Specific Fuel Consumption (BSFC) across a wide range of engine speed and load operating regions, subject to several arrangement schemes for this catalyst converter. It has been indicated from experimental results that the upstream placement of TWC (Three Way Catalyst) ahead of the NOx Adsorber Catalyst is the best solution, which gives rise to the highest converting efficiency to reduce the NOx emission level of the lean burn gasoline engine. The effects of engine speed on exhaust emissions and BSFC are also reflected by operating time of lean mode and rich mode as well as the time ratio between the two using adsorber-reduction catalyst converters. Engine load is in fact the major factor in affecting exhaust characteristics and BSFC of lean burn engines.
This paper presents a thorough analysis of the exhaust gas aftertreatment systems of Gasoline Direct Injection (GDI) engines. The mechanism of the exhaust gas aftertreatment systems is investigated using chemical thermodynamics. The physical models of three-way-catalyst (TWC) and lean NOx trap (LNT) are presented. The objective is to propose an alternative approach for the identification of A/F ratio and oxygen concentration in the exhaust systems to substitute the costly oxygen sensors. A simple control scheme is included within the model identification and prediction results are compared with the testing data from the universal exhaust gas oxygen (UEGO) sensor and from the heated exhaust gas oxygen (HEGO) sensor. The oxygen storage effect has an essential impact on the LNT storage and purge operations, which will also affect the overall fuel economy of GDI engine systems. Its influence on the fuel economy has been estimated by numerical simulations, which is correspondent to the extra percentage of fuel consumption.
An adsorber-reduction catalyst system has been developed for NOx emission control on a lean burn gasoline engine. Its electronic control system can provide different time intervals and variable A/F ratio at lean mode and rich mode. In storage mode, the engine operates at lean burn under rich oxygen environment. In reduction mode, ECU turns down both the throttle angle and ignition timing to provide a stable torque output. This electronic control system is used to investigate the impact of engine speed and load on emission characteristics and fuel economy. It is indicated from experimental results that the upstream placement of TWC (three way catalyst) ahead of the designed NOx adsorber catalyst gives rise to highest converting efficiency to reduce the NOx emission level. The roles of engine speed on exhaust emissions and fuel economy are reflected by operating time of lean burn and rich burn as well as the time ratio between the two regarding this designed catalyst converter. Engine load acts as a major factor in affecting exhaust emission characteristics and fuel economy of the lean burn engine. The heavier the engine load, the higher the NOx emission level, the less the NOx conversion rate, the better fuel economy.
In the absence of online emission measurements, the control of lean burn engine after treatment system is often done in a feedforward fashion based on models of feed gas emissions and the after-treatment subsystems. When the ambient conditions (such as humidity) change or the engine components age, these models are no longer accurate, and the performance of the control system that relies on these models may deteriorate. In this paper, we show how the parameters of a lean NOx trap (LNT) model can be identified online using a conventional switching exhaust gas oxygen sensor to improve robustness of the after treatment control system
In this paper, we present a phenomenological nonlinear dynamic
model for direct injection stratified charge (DISC) gasoline engines and
discuss several key control problems for this advanced technology
powertrain. The model is developed and validated using dynamometer
engine mapping data obtained from a 4-cylinder DISC engine. It captures
the static behavior of the key components of a DISC engine, such as the
torque and emissions generation and volumetric efficiency, as well as
the essential dynamics for the intake manifold and engine rotational
inertia. It is shown that the multimode operation of a DISC engine
dictates a hybrid model structure and also requires a coordinated
multivariable control strategy to achieve expected performance
The design of a temperature control system for a lean NO<sub>x
</sub> trap (LNT) during a desulfation event is described. Lean NO<sub>x
</sub> traps store NOx during lean (fill) A/F operation and
release harmless N2 and O2 during rich A/F (purge)
operation. The presence of sulfur in the fuel poisons the LNT and
reduces its NOx storage capacity. The NOx capacity
can be restored through desulfation. The desulfation method used here
involves sequential A/F ratio modulation of the engine cylinders. This
process generates an exotherm in the LNT. The exotherm must be
accurately controlled to avoid over temperature and damage to the LNT
and under temperature to avoid ineffective desulfation. The control
system described contains both feedforward and feedback elements. Values
for the control parameters were determined through system identification
A control oriented dynamic model of the Lean NO x Trap (LNT) behavior has been developed in SIMULINK TM . The model simulates the trapping and purging phenomena and includes the important parameters which affect the LNT behavior. These include the trap temperature, trapping and purging duration, air fuel ratios and the mass flow rates of the exhaust gases. Engine dynamometer test data have been used to identify the model parameters and to validate the model structure. There is good agreement between the simulation results and test data. The model is suitable for control and fuel / emission tradeoff analysis. 1. Introduction With the increased emphasis on fuel economy improvements, especially in Europe, automotive research and engineering efforts are refocused on Lean burn (LB) and Direct Injection (DI) engines. Lean burn engines typically operate at air fuel ratios of 20:1, while DI engines are operated at air fuel ratios as high as 40:1 during stratified charge mode of operation. ...
Improving the NO /fuel economy tradeoff for gasoline engine with CCVS combustion system
- J Stokes
- T Lake
- M Christle
‘NO emission aftertreatment study on lean burn gasoline engine using adsorber reduction catalyst
- Z Li
- Z Ye
- Y Zhang
- X Sun
- G Zhang