Transient Spark Advance Calibration Approach

Future emission regulations could force manufacturers to install in-cylinder pressure sensors on production engines. The availability of such a signal opens a new scenario in terms of combustion control: many settings that previously were optimized off-line, can now be monitored and calibrated in realtime. One of the most effective factors influencing performance and efficiency is the combustion phasing: in gasoline engines Electronic Control Units (ECU) manage the Spark Advance (SA) in order to set the optimal combustion phase. SA optimal values are usually determined by means of calibration procedures carried out on the test bench by changing the ignition angle while monitoring Brake and Indicated Mean Effective Pressure (BMEP, IMEP) and Brake Specific Fuel Consumption (BSFC). The optimization process relates BMEP, IMEP and BSFC mean values with the control setting (SA). However, the effect of SA on combustion is not deterministic, due to the cycle-to-cycle variation: the analysis of mean values requires many engine cycles to be significant of the performance obtained with the given control setting. This paper presents a novel approach to SA optimization, with the objective of improving the performance analysis robustness, while reducing the test time. The approach can be either used in the calibration phase or in on-board applications, if the in-cylinder pressure signal is available: this would allow maintaining the optimization active throughout the entire engine life. The methodology is based on the observation that, for a given running condition, IMEP can be considered a function of a single combustion parameter, represented by the 50% Mass Fraction Burned (50%MFB). Due to cycle-to-cycle variation, many different MFB50 and IMEP values are obtained during a steady state test carried out with constant SA, but these values are related by means of a unique relationship. The distribution on the plane IMEP-MFB50 forms a parabola, therefore the optimization could be carried out by choosing SA values maintaining the scatter around the vertex. Unfortunately the distribution shape is slightly influenced by heat losses (i.e., by SA): this effect must be taken into account in order to avoid over-advanced calibrations. SA is then controlled by means of a PID (Proportional Integer Derivative) controller, fed by an error that is defined based on the previous considerations: a contribution is related to the MFB50-IMEP distribution, and a second contribution is related to the net Cumulative Heat Release (CHRNET)-IMEP distribution. The latter is able to take into account for heat losses. Firstly, the methodology has been tested on in-cylinder pressure data, collected from different SI engines; then, it has been implemented in real-time, by means of a programmable combustion analyzer: the system performs a cycle-to-cycle combustion analysis, evaluating the combustion parameters necessary to calculate the target SA, which is then actuated by the ECU. The approach proved to be efficient, reducing the number of engine cycles necessary for the calibration to less than 1000 per operating condition.

Prediction of emissions and performance of a diesel engine fueled with n-octanol/diesel blends using response surface methodology

Taguchi-Grey Relational Based Multi-Objective Optimization Of Process Parameters On The Emission And Fuel Consumption Characteristics Of A VCR Petrol Engine

As high exhaust gas recirculation (EGR) is introduced for efficiency, the combustion duration and combustion delay is elongated due to slow fuel burn rates requiring flexible and robust management of both the combustion initiation and duration (what we call combustion shaping). Combustion shaping through cylinder pressure sensing and feedback control of spark advance (SA) and EGR-valve position can be used for spark ignited (SI) engines operating within highly dilute, high efficiency regimes even where the combustion variability (CV) limits controller bandwidth. Although EGR is directly related with combustion duration, spark advance affects the start and duration of combustion simultaneously. This input/output coupling suggests a multivariable controller that coordinates the actuators. Control of SA and EGR is investigated with a coupled linear quadratic Gaussian (LQG) controller and compared with a decoupled proportional-integral (PI) controller. Simulation of the closed-loop system uses a simple engine model derived from system identification. Gain tuning was performed aiming for fast response without overshoot and considering cyclic variability reduction through a Kalman filter. Comparison of the simulated controllers shows that the LQG controller has better transients and responds better to CV.

EGR modeling and fuzzy evaluation of Low-Speed Two-Stroke marine diesel engines

<div class="section abstract"><div class="htmlview paragraph">The increased availability of natural gas (NG) in the United States (US) and its relatively low cost compared to diesel fuel has heightened interest in the conversion of medium duty (MD) and heavy duty (HD) engines to NG fueled combustion systems. The aim for development for these NG engines is to realize fuel cost savings and reduce harmful emissions while maintaining durability. Transforming part of the vehicle fleet to NG is a path to reduce dependence on crude oil.</div><div class="htmlview paragraph">Traditionally, port-fuel injection (PFI) or premixed NG spark-ignited (SI) combustion systems have been used for MD and HD engines with widespread use in the US and Europe. But this technology exhibits poor cycle efficiency and is load limited due to knock phenomenon. Direct Injection of NG during the compression stroke promises to deliver improved thermal efficiency by avoiding excessive premixing and extending the lean limits which helps to extend the knock limit.</div><div class="htmlview paragraph">In this work, a single cylinder engine with 14:1 compression ratio (CR) was used to investigate spark ignited direct injection (SIDI) NG combustion using an integrated spark injector-igniter. Two parameters controlling dilution were investigated (i) increased air charge resulting in an increased air-fuel ratio (AFR) and (ii) exhaust gas recirculation (EGR). The impact of these parameters on fuel consumption, combustion stability, phasing, knock, and emissions of NOx, HC, CO is investigated and reported in this work. Partially stratified combustion (PSC) SOI and SPK timings from previous work will be used as a starting point to investigate the effects. Overall, both AFR and EGR were effective in controlling knock and NOx emissions; however, EGR required lower levels to obtain the desired effect. The use of charge dilution in the PSC range showed promise of trading off knock and combustion stability to within acceptable limits, thus demonstrating potential for increased load operation.</div></div>

Engine efficiency improvement is very critical for medium to heavy-duty vehicles to reduce Diesel fuel consumption and enhance U.S. energy security. The tradeoff between engine efficiency and NOx emissions is an intrinsic property that prevents modern Diesel engines, which are generally equipped with exhaust gas recirculation (EGR) and variable geometry turbocharger (VGT), from achieving the optimal engine efficiency while meeting the stringent NOx emission standards. The addition of urea-based selective catalytic reduction (SCR) systems to modern Diesel engine aftertreatment systems alleviate the burden of NOx emission control on Diesel engines, which in return creates extra freedom for optimizing Diesel engine efficiency. This paper proposes two model-based approaches to locate the optimal operating point of EGR and VGT in the air-path loop to maximize the indicated efficiency of turbocharged diesel engine. Simulation results demonstrated that the engine brake specific fuel consumption (BSFC) can be reduced by up to 1.6% through optimization of EGR and VGT, compared to a baseline EGR-VGT control which considers both NOx emissions and engine efficiency on engine side. The overall equivalent BSFCs are 1.8% higher with optimized EGR and VGT control than with the baseline control. In addition, the influence of reducing EGR valve opening on the non-minimum phase behavior of the air path loop is also analyzed. Simulation results showed slightly stronger non-minimum phase behaviors when EGR is fully closed.

Effect of Exhaust Gas Recirculation (EGR) on performance, emissions, deposits and durability of a constant speed compression ignition engine

<div class="htmlview paragraph">An emissions and performance study was conducted to explore the effects of exhaust gas recirculation (EGR) and multiple injections on the emission of oxides of nitrogen (NOx), particulate emissions, and brake specific fuel consumption (BSFC) over a wide range of engine operating conditions. The tests were conducted on an instrumented single cylinder version of the Caterpillar 3400 series heavy duty Diesel engine. Data was taken at 1600 rev/min, and 75% load, and also at operating conditions taken from a 6-mode simulation of the federal transient test procedure (FTP). The fuel system used was an electronically controlled, common rail injector and supporting hardware. The fuel system was capable of as many as four independent injections per combustion event at pressures from 20 to 120MPa. NOx versus particulate trade-off curves were generated over a range of injection timings for each mode in a baseline condition, then trade-off curves were generated for several of the modes using multiple injections and/or EGR. A previous study, conducted at 1600 rev/min, and 75% of peak torque showed that by using an optimal triple injection, and a 6% EGR rate, NOx and particulate could be simultaneously reduced to as low as 2.2 and 0.07 g/bhp-hr, respectively. The present results first show that at the 1600 rev/min, 75% load running condition, NOx and particulate emissions can be further reduced to 1.58 g/bhp-hr NOx with 0.105 g/bhp-hr particulate by using 10% EGR with an optimized quadruple injection. The present results also show that NOx and particulate emissions as well as fuel consumption can be reduced over the entire engine operating map with the use of multiple injections and EGR. The emissions reductions effected on the test engine, through the use of optimized injection pressures, multiple injections and EGR, allowed an overall cycle emissions reduction from 5.17 g/bhp-hr NOx with 0.44 g/bhp-hr particulate to 3.70 g/bhp-hr NOx with 0.11 g/bhp-hr particulate while providing a reduction in overall cycle BSFC from 206 g/bhp-hr to 184 g/bhp-hr. When corrected to account for the reduced frictional losses of a multi-cylinder engine, these emission levels are in compliance with 1998 US EPA mandates.</div>

A review on low temperature combustion engines: Performance, combustion and emission characteristics

Improving the fuel/air mixing and combustion process in a low-speed two-stroke engine by the IFA strategy under EGR atmosphere

The applications of homogeneous charge compression ignition (HCCI) engine are still limited due to the absence of a definite means to control ignition timing and narrow the operating region. It was found that thermal stratification and charge stratification strategies bring forward good potential to achieve the staged combustion with reduced pressure-rise rates. In this study, a single cylinder engine and a CFD simulation are applied to investigate the combustion processes in the stratified HCCI engine. To obtain thermal and charge stratification on the combustion chamber, exhaust gas recirculation (EGR), glow plug and simulated reformer gas (RG) of CO–H2 mixture are used. Increasing EGR at constant lambda line decreases the maximum achievable power, while at the constant increasing lambda at each constant EGR decreases the indicated mean effective pressure. EGR expands combustion duration hence smoother and quieter operation is achieved. Increasing reformer gas blend fraction considerably expands the operating region toward the lean side. Advancing combustion timing at constant energy flow and intake temperature stem from using glow plug in the combustion chamber, while with increasing mean in-cylinder temperature, combustion duration is prolonged. Abbreviations: 3D: Three-Dimensional; CAD: Crank angle degree; CI: Compression ignition; EGR: Exhaust gas recirculated; HCCI: Homogenous charge compression ignition; NOx: Nitrogen oxides; PM: Particular matter; PRFs: primary reference fuels; RG: Reformer gas; rpm: Revolution per minute; SI: Spark ignition; TB: Third body; THC: total hydrocarbon; UHC: Unburned hydrocarbon

This paper presents some experimental operating and combustion properties of homogeneous charge compression ignition (HCCI) combustion. HCCI operating range, start of combustion, burn duration, indicated mean effective pressure, indicated specific emissions, and indicated specific fuel consumption are evaluated as charge dilution and octane number are varied. Primary reference fuels with octane numbers of 20, 40, and 60 are used in this study. The autoignition properties of the air-fuel mixture are varied by changing the fuel octane number, percentage of exhaust gas recirculation (EGR), and air-fuel ratio, while holding the intake temperature, engine speed, and compression ratio constant. Results show that both the start of combustion and the burn duration are sensitive to mixture dilution (excess air or EGR). The fuel octane number is not an effective method of controlling the start of combustion or the burn duration but can be used to increase the load range of the HCCI engine. Both the NO x emissions and the indicated specific fuel consumption increase as the octane number is increased due to lower dilution and higher peak temperatures. Correct amounts of dilution are critical in controlling HCCI combustion. Separating dilution into EGR and excess air, it is found that a given amount of EGR is more effective at controlling the start of combustion and the burn duration than the same amount of excess air.

The increasing demand for improved efficiency of diesel engines requires more advanced combustion solutions. In addition to traditional methods such as EGR, turbocharging and advanced injection systems, variable valve timing is now available at a reasonable production cost. The use of variable inlet valve timing provides an efficient way for Low-Temperature Combustion (LTC) which provides high thermal efficiency in combination of low emission levels. Furthermore, by modifying the characteristics of the charge air (i.e. by means of EGR, boost pressure and late inlet valve closing, LIVC), further hardware optimization becomes possible, e.g. by increasing compression ratio without reaching critical peak pressures. In the present study, the effect of LIVC was investigated together with the effect of EGR in a single cylinder heavy duty diesel engine. The engine was equipped with pneumatically controlled inlet valves and a high pressure common rail injector. Different injection timings and injection pressures were investigated at two different load points. The mass flow of oxygen was kept constant in order to show how the physical properties (density and temperature) affect the combustion and emission characteristics. The combustion results showed that if the oxygen mass flow is kept constant, EGR is a more efficient way (compared to LIVC) to lower the fuel consumption since it is accompanied with the largest gas flow and thus increased fuel conversion efficiency. The LIVC decreased the fuel consumption at low loads and reduced the emissions at both loads. Transportation of people and goods tend to increase and since internal combustion engines will remain a major power supply for many years to come, reduced fuel consumption is an utmost important way to decrease the CO2 emissions and to move towards a sustainable society. The results in this study show that variable inlet valve timing can be used as one important complementary tool to obtain better combustion characteristics and thus enabling more efficient powertrains.

Calorific value enhancement of fusel oil by moisture removal and its effect on the performance and combustion of a spark ignition engine