Browse Topic: Stratified charge engines

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A Review of Ultra-lean and Stratified Charged Combustion in Natural Gas Spark Ignition Engines03-16-07-00503/15/2023
Natural gas (NG) can be compressed to a high pressure of around 200 bar for use in engines and other applications. Compressed natural gas (CNG) contains 87–92% methane (CH4) and has a low carbon-to-hydrogen ratio compared to other hydrocarbon (HC) fuels. Due to this, it can potentially reduce carbon dioxide (CO2) emissions by more than 20% compared to conventional fuels like diesel or gasoline. This makes CNG one of the most environmentally friendly fuels for internal combustion engines (ICEs). To improve the thermal efficiency of ICEs, higher compression ratios (CRs) and leaner combustion are essential. Since CNG is a gaseous fuel, it has several advantages over liquid fuels due to its favorable physical and chemical properties. A few of these advantages are minimal fuel evaporation issues, a low-carbon content in the fuel composition and a high-octane number. The CNG high-octane number allows for a high CR, resulting in higher thermal efficiency and lower emissions. It should be noted that gaseous fuels, while offering some advantages, also present some disadvantages, such as a reduction in the volumetric efficiency of engines. During the fueling process, when gaseous fuel is introduced to the cylinder through the intake manifold (e.g., through port fuel injection [PFI]), intake air is displaced by the fuel, which reduces the volumetric efficiency of the engine. Through direct injection (DI) technology, spark ignition (SI) engines can achieve greater volumetric efficiency by introducing fuel directly into a combustion chamber. Furthermore, DI fueling reduces the need for throttling to control the engine output power in ultra-lean conditions in addition to stratified charges, which results in improved fuel consumption. A reduction in throttling during engine operation will result in a reduction in pumping losses. During the design and optimization process of an SI engine utilizing DI technology with CNG fuel, the spray formation process, the ignition probability, and the combustion propagation of CNG-DI need to be studied. An in-depth review of CNG fueling strategies for SI engines is presented with a focus on ultra-lean combustion. In this context, the problems associated with ultra-lean combustion of CNG, and their possible solutions will be discussed. This article will be followed by a review on lean combustion of CNG in ICEs using turbulent jet ignition (TJI) as a potential method to solve the problem of lean-burn combustion of CNG with high-energy ignition systems, including TJI.
Ziyaei, Siyamak, Mazlan, Siti Khalijah, Lappas, Petros
Direct-injection resurgenceAUTOJAN05_021/1/2005
The Japanese OEMs are integrating the latest-generation technology into their newest gasoline and diesel engines, focusing the latter on export markets such as Europe. Japan's direct-injection gasoline (DIG) engine movement, at one time touted to be champion of power and fuel economy, may have appeared to have slowed but has not. There are still many vehicles powered by a variety of DIG powerplants. Nissan has the most, comprising direct-injection versions of the QR inline four-cylinder and the VQ V6, all identified with the suffix DD. Mitsubishi suffered from its overly zealous GDI (gasoline direct-injection) drive, turning almost all of its gasoline engines to the specification. The beleaguered manufacturer has persevered, offering some GDI models while readying the improved second-generation version. The DIG movement is now gathering renewed momentum. Toyota and Honda now offer two new cars powered by their latest direct-injection gasoline engines of uniquely different characteristics: Toyota with a stoichiometric-charge-burning V6 and Honda an ultra-lean-burn one.
Yamaguchi, Jack
Reduction of Exhaust Gas Emission in a Two-Stroke Engine with Pneumatic Fuel Injection2002-01-21687/9/2002
In this article possibilities of fuel injection control in two-stroke engines are presented. This is a low cost in-cylinder fuel injection system for stratified charge engines according to idea of Professor Stanislaw Jarnuszkiewicz with modified system of gases movement organization, that is much simpler than alternatives. The authors modified this pneumatic fuel injection system by means of hot exhaust gases drawn from one cylinder during the working stroke and, following the addition of fuel, forced into another cylinder during the compression stroke. Spraying and injection of fuel by means of hot exhaust gases give additional possibilities of complete evaporation of light fuels, alternative fuels with extended fraction and heavier fuels, such as diesel oil, kerosene and vegetable oil. In the combustion system presented the process of preparing liquid hydrocarbon fuel for combustion is one of the main factors influencing the efficiency of the conversion of chemical energy contained in the fuel to mechanical energy. The most significant is the fuel phase transition, and especially a repeatability of the fuel dose per cycle. This process is inseparably associated with the physical properties of fuel, and changes of rate of pressure in gas duct. In practice, a two-stroke internal combustion engine with spark ignition and pneumatic injection accomplished by means of exhaust gases successfully uses liquid fuels with very different fractional and group composition, which may be very beneficial from the viewpoint of practical realization of utilization processes. The results of tests shown it is possible to reach a high repeatability of the fuel dose per cycle and maintaining uniform fuel doses for each cylinder.
Marek, Wojciech, Mitianiec, Wladyslaw
Fundamental Research on Unsteady Pre-mixed Combustion in Non-Uniform Distribution of Fuel Concentration2001-01-34879/24/2001
It is significant for understanding the phenomena in a stratified charge engine and an SI engine with direct injection system to carry out the fundamental research. The experiments were conducted in a constant volume chamber with atmospheric condition. The pre-mixed charge composed of ethylene and air was charged with various equivalence ratio, the second charge with the same composition was injected into the chamber, thereafter, the combustion started by a spark plug. The phenomena were analyzed by use of the experimental results of shadowgraph, [OH] natural emission, pressure history and NOx and UHC in the exhaust gas.
Fujimoto, Hajime, Senda, Jiro, Sano, M., Azechi, N., Okumi, M.
The Influence of Dilution Composition and Temperature Upon a Stratified Charge Spark Ignition Engine2000-01-19476/19/2000
A thermodynamic model has been utilised in the analysis of a SI engine operating with a divided charge stratification system. Such a charge stratification system divides the cylinder charge into two distinct regions: a combustible charge around the spark plug and a dilution charge beyond this. The model has been utilised to reveal differing effects of both dilution charge composition (EGR or air) and temperature upon the performance and emissions of such a stratified charge engine.
Calnan, Peter, Zhao, Hua, Ladomattos, Nicos, Ma, Tom
Twice Electronic Fuel Injection (TEFI)--A New Idea of Lean Combustion in S.I. Engines [ 1 ]2000-01-10873/6/2000
A new idea for realizing lean burn combustion with the low pressure port injection technique in S.I. engines, the technique of TEFI (Twice Electronic Fuel Injection per cycle), is proposed. That is, the total amount of fuel needed for each cycle is divided into two parts and injected at different timings to adjust and optimize the air and fuel mixture strength distribution in the cylinder. As a result, the air and fuel mixture strengths both at the spark plug region and in the whole cylinder can be adjusted arbitrarily. Therefore a lot of problems present in the conventional stratified charge engines can be avoided. Through the lean combustion experiment on a 5 valves EFI S.I. engine using the swirl control valve “SCV” technique, the advantages of the TEFI are confirmed.
Shuliang, Liu, Yongjian, Fan, Pucheng, Pei
Analysis of a Stratified Charging Concept for High-Performance Two-Stroke Engines2000-01-09003/6/2000
This paper presents the results and conclusions from a conceptual design study for a stratified charging concept. The stratified charging engine has a displacement of 64 cm3 and a four-port design with reed valves at two ports to control the bypass air. During the intake stroke of the engine, bypass air is sucked into the transfer ports to purge the air-fuel mixture present in the ports from the previous stroke back into the crankcase. This fills the transfer ports near the exhaust with pure air at the beginning of the scavenging stroke. During scavenging, the bypass air is ejected in the cylinder, shielding the exhaust against the fresh mixture coming from the ports on the intake side. This allows the hydrocarbon emissions to be reduced by over 40 %. The conceptual design study is based on an analysis of the mixture short-circuiting mechanisms and CFD investigations of the scavenging flow with charge stratification.
Zahn, Wolfgang, Rosskamp, Heiko, Raffenberg, Michael, Klimmek, Axel
A Turbulent Combustion Model for a Stratified Charged, Spark Ignited Internal Combustion Engine2000-01-02753/6/2000
A turbulent combustion model is described for SI engines with large variations in mixture strength. The model is for a single gas phase fluid at high Reynolds number and treats combustion in the laminar flamelet regime, which is characterized by high Damkholer and low Karlovitz numbers. An assumed probability density function (pdf) approach is used to extract expressions for mean quantities of interest, which are parameterized on the progress variable and mixture fraction variables. A double delta function pdf is used for the reaction progress variable and a beta function pdf is used for the mixture fraction. The reaction rate term in the progress variable equation is closed using an algebraic expression, which incorporates the effects of mixture strength, pressure and temperature on laminar flame speed. The model is implemented in two versions of a Computational Fluid Dynamics (CFD) code. The first version simulates reciprocating engine flows and the second simulates combustion in closed vessels. Comparison is made against published experimental data for an engine running a homogeneous charge. Agreement with this experimental result is good based on limitations and assumptions used. Qualitatively predictions of combustion trends in stratified charge engines and closed vessels also show agreement with experiment. However, further validation is required with experimental engine data for stratified charge engines.
Ranasinghe, John, Cant, Stewart
Investigation of the Fuel Distribution and the In-cylinder Flow Field in a Stratified Charge Engine Using Laser Techniques and Comparison with CFD-Modelling1999-01-354010/25/1999
This paper presents an investigation of a Volvo Direct Injection Spark Ignition (DISI) engine, where the fuel distribution and the in-cylinder flow field have been mapped by the use of laser techniques in an engine with optical access. Along with the experimental work, CFD-modelling of flow and fuel distribution has been performed. Laser Induced Fluorescence (LIF) visualisation of the fuel distribution in a DI-engine has been performed using an endoscopic detection system. Due to the complex piston crown geometry it was not possible to monitor the critical area around the sparkplug with conventional, through the piston, detection. Therefore, an endoscope inserted in the spark plug hole was used. This approach gave an unrestricted view over the desired area. In addition, the in-cylinder flow fields have been monitored by Particle Image Velocimetry (PIV) through cylinder and piston. The results from both the LIF and the PIV measurements have been compared with CFD-modelling at Volvo. The validation was made at part load when the engine was operating in stratified mode, i.e. late injection during the compression phase. Qualitative agreement was found between the calculated and measured fuel distribution around the spark plug prior to ignition. Also the PIV measurements showed a promising agreement with the flow fields obtained by CFD-modelling. In addition, the transportation properties of the fuel distribution that was monitored by LIF could to a great extent be explained by the results from the PIV measurement and the CFD-modelling. All three techniques showed promising agreements with each other and the measured properties could be used to further increase the accuracy of the CFD-modelling. The close collaboration and comparison between different techniques described in this paper increased the understanding of the processes going on in the combustion chamber.
Richter, M., Axelsson, B., Aldén, M., Josefsson, G., Carlsson, L-O., Dahlberg, M., Nisbet, J., Simonsen, H.
Can the Best Fuel Economy of Today's Engines Still Be Improved?9819128/11/1998
Direct injection into open chambers of Diesel- and S.I.- Engines is considered by the experts of automotive engineering worldwide as the best way for future economy and ecology engines [1]. Beside of the best fuel saving passenger cars driven by Diesel engines, advanced Diesel like Stratified Charge Engines as the CCSC (Controlled Combustion Stratified Charge) and the MESC (Mixture Exhaust Stratified Charge) -Engines open the way for future developments. Both engines work with the following new elements: Air assisted injection for the formation of the combustible mixture in the small cavities of prechambers, where the load control is achieved by the quantity of the injected fuel without the need of throttling the charge of the main chamber as common in today's SI engines. Pulsed Jet Combustion, where at first in small cavities of prechambers a rich mixture gets ignited. Afterwards pulsed jets of burning gases, at least two jets moving in opposite directions, impinge each other in the middle of the cylinder, where after a sudden multipoint ignition a fireball-combustion of lean mixture takes place, surrounded by a layer of inert gases close to the cylinder wall. Stratification of residual gas, in order to reach an isolation of the burning lean mixture to avoid heat losses and flame quenching at the wall. In this procedure only that amount of formerly burnt residual gas gets discharged from the cylinder, which equals the amount of the newly formed burnt gas coming from the fireball. In a cooperative investigation at the Technical University Poznan and the Institut für Fahrzeugbau in Wolfsburg, sponsored by the Volkswagen Foundation, theoretical and experimental results showed the successful application of the MESC-principle on reciprocating engines.
Heitland, Herbert, Rinne, Gerhart, Wislocki, Krzysztof
Can the No Man's Land Between Diesel- and Otto-Engines be Bridged?9519628/1/1995
In modern Diesel engines at the best point a theoretical thermal efficiency up to 50% can be reached and, with supercharging, it is possible to obtain mean effective pressures comparable to those of Otto engines. In spite of this successful development, power density, partload behavoir, pollutant emissions and noise levels are still too high to fulfill future environmental demands. With so called hybrid engine concepts, a combination of procedures of Otto- and Diesel engines, so far only a marginal improvement of today's Otto- and Diesel engines could be reached. With a completely new design of stratified charge engines, iniated by pulsed jets generated by combustion of rich mixtures in pre chambers and followed by fireball-combustion of lean mixtures in the middle of the cylinder, surrounded by a layer of inert gas close to the cylinder wall, a quantum transition can be reached with diesel-like stratified charge engines, with which it would be possible to avoid any kind of exhaust gas-after-treatment. Results of computer simulation have shown that two-stroke-engines have the best potential.
Hauser, G., Heitland, H., Wislocki, K.
Combustion and Emissions in a New Concept DI Stratified Charge Engine with Two-Stage Fuel Injection9406753/1/1994
A new concept DISC engine equipped with a two-stage injection system was developed. The engine was modified from a single cylinder DI diesel engine with large cylinder diameter (135mm). Combustion characteristics and exhaust emissions with regular gasoline were examined, and the experiments were also made with gasoline-diesel fuel blends with higher boiling temperatures and lower octane numbers. To realize stratified mixture distribution in combustion chamber flexibly, the fuel was injected in two-stages: the first stage was before the compression stroke to create a uniform premixed lean mixture and the second stage was at the end of the compression stroke to maintain stable ignition and faster combustion. In this paper, the effect of the two-stage injection on combustion and exhaust emissions were analyzed under several operating conditions. The results showed that stable and smooth combustion without knocking over a wide range of operation could be realized in the new concept DISC engine, and compared with stoichiometric homogeneous combustion at a BMEP of 0.61 MPa, simultaneous 30% SFC and 50% NOx reductions were achieved. The SFC and NOx were reduced remarkably not only in the lean conditions but also in the stoichiometric conditions by the stratified charge combustion with the two-stage injection. Optimization for spark timings, secondary fuel injection timings, the proportion of two-stage fuel injection, and the number of nozzle holes was essential for efficient combustion and ignition. Smokeless and knockfree operation could also be achieved with higher boiling temperature and lower octane number fuels. Soot was not detected even with gasoline containing 50vol.% diesel fuel. The NOx emission from compression ignition CI engines has become a serious problem in urban environments and globally, and strict regulations may force the conversion of some CI engines to spark ignition SI engines if CI engine emission countermeasures remain insufficient. Such conversion presents two problems in SI engines however: (1) a deterioration in thermal efficiency, and the exhaust contributes to the greenhouse effect, (2) limitations in cylinder diameter resulting in knocking especially in large size engines. Also the middle distillation component of petroleum, the diesel fuel, will be in excess, so that utilization of wide cut gasoline with higher boiling temperatures and lower octane numbers will be desired. To improve the thermal efficiency of SI engines, lean combustion assisted by tumbling or swirling air motion in the combustion chamber has been reported and already put to practical use[1, 2 and 3]. A DISC combustion is usually more effective to improve thermal efficiency and also offers the potential of knockfree operation and utilization of a wide-range of fuels. Despite much work, ordinary types of DISC engines have difficulty in achieving stable and efficient combustion. However, if the fuel injection is flexible, a possibility with today's technology, DISC engines can be expected to achieve more stable combustion, lower exhaust emissions, higher thermal efficiency, and higher output over the whole range of operation. In this research, a new concept DISC engine with a “two-stage fuel injection system” was developed. To realized desirable combustion characteristics, lower emissions, and higher thermal efficiency and power, the stratified mixture distribution in the combustion chamber was controlled flexibly with two-stage fuel injection: the first stage was set before the compression stroke to create a uniform premixed lean mixture and the second stage at the end of the compression stroke to maintain stable ignition and efficient combustion. Combustion characteristics and exhaust emissions with regular gasoline were examined, and the experiments were extended to the gasoline-diesel fuel blends with higher boiling temperatures and lower octane numbers.
Miyamoto, Noboru, Ogawa, Hideyuki, Shudo, Toshio, Takeyama, Fumiaki
An Experimental Investigation on Air-Fuel Mixture Formation Inside a Low-Pressure Direct Injection Stratified Charge Rotary Engine9306783/1/1993
Stratified charge engines have been getting attention for the drastic improvement in thermal efficiency at low-load region. There have been researchers on the two types of engines-the high pressure direct injection stratified charge type in which fuel is supplied directly at high pressure into its combustion chamber right before ignition timings, and the low pressure direct injection stratified charge type in which fuel is injected directly into its cylinder while the cylinder pressure is comparatively low[ 1- 3]. Rotary engines have higher freedom than reciprocating engines in terms of equipping direct fuel injection devices, since their combustion chambers rotate along the rotor housing. The fuel supply units, therefore, need not be exposed to high temperature combustion gas. Realization of the low pressure direct injection stratified charge (hereafter “LDISC”) engine is, however, almost impossible without comprehensive understanding of flow fields, because the air-fuel mixing time of this kind of engine is much longer than that of high pressure injection type engines, and hence the flow fields are supposed to give more effect on the mixing process. There have been several reports on the flow fields of peripheral inlet ported rotary engines from the report made by Yamamoto et al. [ 4] to computational or visualization studies including by the authors[ 5- 8]. Although there have been some computational studies on the flow fields of side ported rotary engines, they focuses on the flow inside a supercharged direct injection stratified charge rotary engine[ 9] at higher intake pressure than that of this study or inside a primixed-charge natural-gas-fueled rotary engine mainly of near top dead center[ 10]. Thus, the flow fields of side ported rotary engines have not been revealed adequately. The desirable state of stratification in rotary engines is considered to be the stratification of air-fuel mixture in the leading side of combustion chambers. This is because: out of two ignition plugs installed one on the leading side (hereafter “L-side”) and one on the trailing side (hereafter “T-side”) of the combustion chamber, the ignition plug on the L-side has larger opening area and hence better ignitability than the T-side plug, and the poor flame propagation on the T-side of the combustion chamber due to the effects of wall quenching and squish flow. In this study, to observe the flow-fields and the air-fuel mixing process of a side ported LDISC rotary engine from intake to compression stroke, a transparent single-rotor engine was designed. Not only does the paper provide visualized flow fields, but also shows some results from combustion analysis made on an actual engine with same geometries and timings.
Hasegawa, Yasuaki, Yamaguchi, Kouichi
Mixture Formation and Combustion in a Spark Ignition Engine with Direct Fuel Injection9205212/1/1992
This paper presents investigations on the combustion process in a single cylinder SI engine with direct injection. Different nozzle types are examined i.e. hollow cone nozzles and hole type nozzles both with different geometry of the injected spray. These nozzle types have been compared in view of their suitability of creating a homogeneous as well as a stratified mixture in the combustion chamber. To create a homogenous mixture, the fuel was injected during the intake stroke. In order to examine the homogeneity of the mixture in the case of direct injection, the engine was driven with mixture formation generated through intake port injection. The comparison of the direct injection method with the intake port injection for homogenous mixture formation has shown only small differences in engine behavior. To create a stratified mixture in the combustion chamber, the fuel was injected at the end of the compression stroke. In the case of a low swirl level, the hollow cone nozzle with a cone angle of 120° leads to a stratified mixture. With this nozzle the engine could be driven until relative air/fuel ratios of about four. With the six-hole nozzle (120° spray angle) and a significant higher swirl level, a stratified charge engine behavior could also be realized. The minimum fuel consumption is reached with the 120° hollow cone nozzle.
Spiegel, L., Spicher, U.
Visual Study of Diffusion Process of Impinging Spray in Stratified Charge Engine Using Liquid-Liquid Injection Technique91245711/1/1991
In order to clarify a diffusion process of impinging spray on a direct fuel injection in a stratified charge engine, visual observation was made on the diffusion processes of fuel after impingement, by using a liquid-liquid injection technique by means of a single shot photography. Furthermore, the performance of actual engine adopted a impinging diffusion method was examined by using a small direct injection(D.I.) diesel engine. In this technique, the liquid fuel was injected into a plastic piston cavity which was filled with water to simulate the diffusion process of fuel after impinging against a cylindrical target vertically provided at the center of the piston cavity. The impinging spray radially diffused from the target center and formed a torus, which was viewed from the bottom and the side. The results suggest that a practical application of stratified charge engine to the small D.I. diesel engine with twin valves and an inclined injection nozzle is possible by making the end surface of target incline.
Watanabe, Takashi
The Development of a Stratified Charge Rotary Engine Apex Seal Material9106272/1/1991
The rotary engine has evolved into an alternate power source, along with the reciprocating engine and is finding many applications including automotive, industrial, and military. Recent advances in rotary engine technology include development of stratified charge engines with multifuel capability. These engines operate at higher peak pressures than the homogeneous charge type and require higher component mechanical strength properties and improved wear resistance for the sliding surfaces. The apex seal makes line contact with the rotor housing surface and, more than any other seal in the engine, is subjected to high contact loads and sliding surface temperatures which make it susceptible to high rate of wear. Combustion chamber pressure tightness, and thus engine performance, depend to a great extent on the apex seal wear. This requires that the phenomena associated with seal wear be studied carefully before a proper seal material can be selected. The paper presents the design and use of a rig to study the seal wear under approximate engine simulation conditions and describes the development and evaluation of a new seal material made as a result of the rig tests.
Revankar, G. S.
AFR and Emissions Calculations for Two-Stroke Cycle Engines9015999/1/1990
This paper demonstrates the very useful technique of calculating air-to-fuel ratio, AFR, from exhaust gas emissions for a two-stroke cycle engine. Such methods are widely used for four-stroke engines where direct air flow measurement has now become redundant. Two modified methods are presented and compared with three standard methods, showing the accuracy to be quite good for a large set of test data from a standard two-stroke engine. A procedure for estimating AFR of the in-cylinder burning region, using trapping efficiencies, is presented for stratified charge engines, such as those with direct fuel injection. Accuracy of emissions measurement is assessed by calculating the total dry exhaust emissions, a method which could easily be automated for general test cell use. Finally, exhaust gas molecular weight and wet/dry ratio calculations are considered.
Douglas, Roy
Location of Peak Pressure for an Axially Stratified-Charge Engine8700806/1/1987
Characteristics of the cylinder pressure waveform have long been considered for optimizing the operation of automotive engines. In particular, the strategy of maintaining a constant crank angle location of the peak cylinder pressure (LPP) during combustion has been predominant in the reported studies. This technique was therefore evaluated for an existing minimum fuel consumption calibration of an experimental axially stratified-charge (ASC) engine. For the ASC engine the LPP responded to spark advance and exhaust gas recirculation changes in a similar manner to that of a homogeneous-charge engine; LPP decreased with spark advance and increased with exhaust gas recirculation. However, the LPP for the predetermined minimum fuel consumption calibration of the ASC engine varied over a range of 8° to 19° after top dead center (ATDC) under steady state conditions. This is in contrast to the nearly constant 15° ATDC LPP observed by others for most homogeneous-charge engines. In light of the increased compression ratio and charge dilution used on the ASC engine, as well as the stratified-charge nature of the engine, the wide range of LPP experienced is not surprising. Chassis dynamometer and road test results of a vehicle equipped with the ASC engine were largely in agreement with the steady-state observations. It is concluded that controlling the LPP at a single value is inadequate as a simple calibration or control method for the axially stratified-charge engine.
Chang, Man-Feng, Stevens, James E.
Performance and Combustion Modeling of Heterogeneous Charge Engines8503432/1/1985
This paper reviews the phenomoneological modeling of the combustion processes for the diesel and fuel-injected stratified charge engines. Distinctions are made between phenomenological and multi-dimensional finite-difference approaches. The modeling methodologies and the basic components in these models are described. These include characterization of the fuel spray, fuel-air mixing, ignition, burning and heat transfer processes. An attempt is made in the paper to highlight the similarities and contrasts of various models and relate to their utility in addressing emission research and engine performance development objectives.
Primus, Roy J., Wong, Victor W.
Application of a Mini-Dilution Tube in the Study of Fuel Effects on Stratified Charge Engine Emissions and Combustion81119810/1/1981
A mini-dilution tube to measure particulate emissions is described and results obtained in an application are presented. The application selected is a study of fuel effects on stratified charge engine emission and combustion characteristics. The mini-dilution tube was developed to provide a capability for particulate measurements with dynamometer engines. The device has been demonstrated to yield particulate mass results agreeing to within 10 percent of those with a full scale tunnel in steady state tests with diesel powered vehicles. A PROCO engine modified by incorporation of Torch Ignition was used in the study. Fuels were a wide cut gasoline, methanol and Indolene Clear gasoline. The engine was operated at a speed of 1250 rpm with an indicated mean effective pressure of 390 kPa. Spark timing, injection timing, EGR and equivalence ratio were varied. Gaseous and particulate emissions and combustion characteristics of the wide cut gasoline and Indolene Clear were found to be nearly identical. with methanol the HC, NOx and particulate emissions were lower than with the gasolines but CO was higher. Combustion rates with methanol were higher than with the gasolines.
Harrington, J. A., Yetter, R. A.
On the Propagation of Turbulent Jet-Flame in a Closed Vessel8107776/1/1981
In the stratified charge engine with an auxiliary chamber, the time required for combustion in the main chamber is considered to depend upon the characteristics of the turbulent jet-flame propagating in it. This study has been conducted to explore the controllability of the time required for combustion by changing the characteristics of the turbulent jet-flame. Experiments were performed by using a constant volume combustion chamber which was divided into a primary and a secondary chamber by an orifice plate. The characteristics of the turbulent jet-flame were changed by changing fuel, mixture strength and hole size of the orifice plate. The experimental results indicate that the time τ required for combustion in the secondary chamber mainly depends upon the jet-flame velocity VF (propagation velocity of the leading front of the jet-flame) and the mixture strength Φ. It is shown that a unique relation exists between VF and (τ SL)−1, were SL is the laminar burning velocity of the mixture, except for rich mixtures of propane-air and n-butane-air.
Furukawa, Junichi, Gomi, Tsutomu
Predictions of Combustion, Fuel Economy, and Emission Characteristics Influenced by the Gas Exchange Process of S. I. Engines8108216/1/1981
The conflicting problems of fuel economy and NOx emissions in a spark ignition engines are discussed in relationship to the residual gas, volumetric efficiency and pumping loss as predicted by the gas exchange analysis which was described in a previous report (SAE P. 800535) . Predictions are made of : (1) the optimum valve timing for obtaining maximum volumetric efficiency; (2) the effect of valve timing on the residual gas and intake air charge and their relationships to the power output, fuel economy, and NO emissions; (3) the influence on combustibility and emissions of the main and auxiliary combustion chambers of a stratified charge engine; (4) the effects of the auxiliary intake valve air jet on the combustion of the lean combustion engine; (5) the effect on fuel economy of decreasing the pumping loss by adjusting valve timing and by adding EGR. These applications of the gas exchange calcualtions indicate the importance of the simulation model in evaluating combustibility, fuel economy, and emission characteristics.
Tasaka, Hidenori, Matsuoka, Shin
Enhanced Ignition for I. C. Engines with Premixed Gases8101462/1/1981
The development of lean charge, fast burn engines depends crucially on enhanced ignition, since one can obtain thereby proper means for increasing the rate of burn in mixtures characterized notoriously by low normal burning speeds. Enhanced ignition involves not only high energies and long duration of ignition, but also a wide dispersion of its sources, so that combustion is carried out at as many sites throughout the charge as possible. Upon this premise, various ignition systems for I.C. engines, operating with premixed charge, are reviewed. The systems are grouped within the following categories: (1) high energy spark plugs; (2) plasma jet igniters; (3) photochemical, laser, and microwave ignition concepts; (4) torch cells; (5) divided chamber stratified charge engines; (6) flame jet igniters; (7) combustion jet ignition concepts; (8) EGR ignition system. The first three derive the power from electrical energy, the rest are powered by exothermic chemical reactions at a significantly lower, practically negligible, fuel consumption. The review emphasizes the concept of staging the processes of initiation and propagation of combustion. Relative positions of various ignition systems is expressed on the plane of relative energies (the ratio of energy consumed by the ignition system, or contained in a pre-chamber, to that of the compressed charge in the main chamber) and relative volumes (the ratio of the volume of the pre-chamber to that of the compressed charge). In principle, ignition systems for engines operating with premixed charge lie on the half-plane of relative energies below one, between 10-5 for standard spark plugs to 10-1 for divided chamber stratified charge engines, while their relative volumes extend from 0 for spark igniters to 0.2 for stratified charge engines. This suggests that proper compartmentization of the combustion process may lead to significant improvements in both pollution emissions from the cylinder and specific fuel consumption of I.C. engines.
Dale, J. D., Oppenheim, A. K.
Raman Spectroscopy and Flow Visualization Study of Stratified Charge Engine Combustion8001362/1/1980
Transient, precombustion fuel/air ratios at the spark plug electrode gap in a DISC engine have been measured using cw laser Raman spectroscopy and have been correlated with mixture ignitability measurements. From these measurements, it was found that with decreasing quantities of injected fuel there was a general trend towards decreased peak equivalence ratio, a delay in fuel arrival at the spark electrode gap, and a narrowing of the crank angle duration over which mixture ignition was possible. Lean inflammability limits determined from the ignition study suggested a dual-ignition mechanism which depended on the rate of change of equivalence ratio with crank angle. Flow visualization of the stratified charge combustion revealed substantial differences in mixture burn characteristics and combustion duration as the ignition crank angle was varied. Quenching of the burning mixture was observed and its occurrence was correlated with the Raman measurements.
Johnston, Sheridan C.
The Volkswagen Lean Burn PC-Engine Concept8004562/1/1980
Results from the 1600 cm3 PCI- (PreChamber Injection) Stratified Charge Engine with a divided combustion chamber and fuel injection into the prechamber were described in SAE Paper 750 869. The main objective of continued development on this engine was to meet future emission and fuel economy standards for European countries with a simpler concept than required in the US, but equally effective. This work lead to the lean burn PC- (Pre Chamber) engine, where the prechamber fuel injection system is omitted. The main part of the program was concerned with the optimization of the PC-Combustion Process, however, the effects of the engine periphery were also considered in detail. A large number of combustion chamber parameters were thoroughly investigated on a 1300 cm3 four-cylinder water-cooled inline engine. Ignition system parameters were included in the test program because they can significantly influence the combustion process. Since an engine concept had to be developed, a large part of the experimental work dealt with fuel-air-mixture formation, distribution and heating. A simple means of exhaust gas after-treatment was also considered in the concept. Exhaust emissions and fuel consumption were evaluated in a number of vehicle tests according to European test procedures. Results show that future European exhaust emission standards, if not too severe, are likely to be met without catalytic after-treatment. No significant problems have been encountered thus far, however, more durability testing needs to be done.
Brandstetter, Walter
Performance of a Stratified Charge Engine7904342/1/1979
An experimental study of a single-cylinder direct-injected stratified charge engine is described, with emphasis upon influences of configuration and injection system details upon performance and exhaust emissions.
Wood, C. D.
Energy Economics of Alternate Fuels7904302/1/1979
The energy crisis of the mid-1970's released a frantic search for alternative fuels. The present paper reviews the studies undertaken by the Author's Company and outlines experience with broad specification fuels, vegetable oils and alcohols. Tests were undertaken mainly with the diesel engine and its derivatives in mind. It is concluded that, in the medium term, the most effective engine/fuel combination is an injected stratified charge engine burning “wide-cut” fuel oils. Such oil could be obtained by a modification to present natural crude refining practices, or from shale and tar sand distillation, or by coal gasification and hydrogenation, or from oil bearing vegetation. Unfortunately, the energy scene is currently confused by the conflict between short term economic gain and long term conservation needs. As a result attention is being focussed on gasolene-like alternatives, notably methyl and ethyl alcohol. As a consequence it is thought that carburetted stratified charge engines, burning alcohol-based or alcohol extended fuels, are likely to become dominant in the mobile prime mover field. It is to be hoped that progressive depletion of natural crudes will promote the gradual introduction of a more efficient combination based on an injected stratified charge engine. In any case, eventual shortages of natural fuels will have far reaching implications on the choice of materials for both engine and vehicle manufacture. Government legislation and taxation policies will also be affected.
Bertodo, R.
Multi-Dimensional Heat Flow in the Surroundings of a Pre-Chamber Under Transient Conditions7904372/1/1979
The gas side wall temperatures of the prechamber in a divided chamber diesel or stratified charge engine have an influence on the combustion process. From this results an important effect on exhaust emissions, fuel economy and engine performance. The insulation characteristic of a prechamber insert should ensure a quick warm-up after cold start on one hand but provide not too high temperatures at full load and maximum engine speed on the other. Computations were carried out to quantify the effects of various design parameters and materials on temperature, heat flow, stress and deformation and to optimize the design under numerous existing restrictions. An analysis was made of the elasto-plastic behaviour of the insert and the cylinder head, including material creep. For most of the calculations a rotary symmetric model was assumed and solved by the finite element program system MARC. The two-dimensional mesh chosen describes the actual details of the section of the cylinder head, the prechamber insert and the spark plug or fuel injector fairly closely. The gas temperature and the heat transfer coefficient were determined from a separate engine cycle simulation. Preliminary calculations with a one-dimensional model of a composite wall were made in order to optimize the mesh in regard to accuracy and computing time. The main cases studied were the following: a prechamber without an insert (base case), an insert insulated by an air gap and being in contact with the cylinder head over a small or larger press fit region, total loss of contact with the cylinder head, a cylindrical insert with and without air gaps, copper alloy and a ceramic as insert material, while stainless steel was used in all other cases.
Brandstetter, W., Birth, M., Stuart, P.
Precombustion Fuel/Air Distribution in a Stratified Charge Engine Using Laser Raman Spectroscopy7904332/1/1979
The application of cw laser Raman spectroscopy to determine precombustion fuel/air distribution in a motored, direct-injected stratified charge (DISC) engine has been demonstrated. The primary objective of the study was to obtain point measurements of the mean, gas-phase fuel/air ratio across a diameter in the combustion chamber for a single set of engine operating parameters. A secondary objective was to obtain flow visualization records of the injection-mixing process for both liquid- and gas-phase fuel injection. Results of the study showed that large spatial variations in the fuel/air ratio occur in the cylinder during and after fuel injection. Near top-dead-center, fuel/air mixing was nearly complete, but the distribution across the cylinder diameter still exhibited a region of relatively low fuel concentration.
Johnston, Sheridan C.
A New Combustion System in the Three-Valve Stratified Charge Engine7904392/1/1979
Through continued research on the combustion system of the stratified charge engine, we have found a new combustion system (named Branched Conduit system) which is able to further reduce exhaust emissions, HC and NOx, in particular with no adverse effect on fuel consumption under the wide range of engine operating conditions. In this paper, we describe the construction of new combustion system and its characteristics including fuel consumption and exhaust emissions. In addition, the combustion process with or without the branched conduits is examined by the time-resolved measurements of gas pressure and temperature obtained in the main combustion chamber, and observed with high-speed colored photography.
Yagi, Shizuo, Fujii, Isao, Nishikawa, Masayasu, Shirai, Hiroshi
Emissions and Economy Potential of Prechamber Stratified Charge Engines7904362/1/1979
In order to meet stringent government emissions standards without penalizing the fuel economy of gasoline engine cars, a number of alternative engine concepts have been investigated. This paper describes a research investigation and parallel development activity on prechamber stratified charge engines. Single-cylinder engine investigations are first described. Alternative design and operating parameters are investigated and compared in these engines. Design and development of two multicylinder engine designs incorporating prechamber 3-valve configurations is next described. Finally, a car development and evaluation program is outlined, using both small and large cars with alternative engine configurations and after treatment devices. Results of the above prechamber stratified charge engines are compared with conventional engines in order to assess and evaluate the emission and economy potential of this type of engine. The authors conclude that this type of stratified charge engine possesses NOx emission and fuel economy performance similar to a conventional engine but at a high HC emission level.
Dimick, David L., Genslak, Stanley L., Greib, Ronald E., Malik, Marvin J.
Unthrottled Open-Chamber Stratified Charge Engines7803412/1/1978
Performance and exhaust emissions of five unthrottled open-chamber stratified charge engine designs are compared on an equivalent basis, to illustrate the effects of the different strategies used to mix the fuel and air and to provide data useful for those currently engaged in stratified charge engine development.
Wood, Charles D.
Simulation of Thermodynamic Cycle of Three-Valve Stratified Charge Engine7803192/1/1978
This paper describes the development of a mathematical model for the compression, combustion, expansion, exhaust and intake processes of a three-valve stratified charge engine. After calculating the mixture formation at the end of compression process, a simple combustion model was developed to compute the gas temperature, gas pressure and the rate of formation of NO and CO at each crankangle, using basic energy and reaction kinetic equations for both the auxiliary and main chambers. The evaluation of the model was carried out by comparing the computed and experimental data. A satisfactory correlation was observed between them.
Asanuma, T., Babu, M. K. Gajendra, Yagi, S.
Efficiency and Emissions of a Stratified Charge Engine Optimized for Various Fuels7802362/1/1978
Experimental work was done with a Texaco stratified-charge engine to investigate the effect of fuel type, spark timing, and fuel injection timing on efficiency and emissions. Gasoline, diesel fuel, and a mixture of the two in equal proportions were used as fuels. The mixture of gasoline and diesel fuel simulates a broad-boiling-range fuel, referred to as “broadcut fuel.” Data were taken during full-load and part-load operations; the part-load operation simulated road-load conditions for a 3,000-lb vehicle. Results show engine efficiency ranges from about 20% at light-load to over 30% at full-load. The difference in efficiency attributable to fuel type was one to two percent. Between the two fuels gasoline and diesel, greater efficiency was associated with diesel fuel at part-load while the greater efficiency at full-load was seen with gasoline. Broadcut fuels generally resulted in efficiencies similar to the efficiencies of operation with diesel fuel at part-load or with gasoline at full-load. The results for all fuels show that spark timing set equal to fuel injection timing generally produced the best efficiency and, except for nitrogen oxides, the lowest emissions.
Evers, L.W., Fleming, R.D., Hurn, R.W.
Prime Movers for Future Lift Trucks7807522/1/1978
An examination of future trends in lift truck developments suggests a stable product line with a requirement for increased power at a time of escalating fuel costs. Within the time scale of the present survey (up to about the year 2000) only battery/electric and derivatives of conventional reciprocating engines will provide this power. As the turn of the century is approached, a breakthrough in the development of high density, low weight battery systems is forecast, leading to a recovery of lost market share and eventual dominance. In the intervening period gasolene and diesel-derived engines will increase their market penetration, but the opportunity of reducing, or at least containing, operating costs by the introduction of a broad specification fuel oil and injected stratified charge engines will be lost.
Bertodo, R., Smith, P.
The Fundamental Research of Combustion in the Stratified Charge Engine With An Auxiliary Chamber7850961/1/1978
The major features of the stratified charge engine with an auxiliary chamber are: (1) the mixture in the combustion chamber has concentration gradient due to the auxiliary chamber and (2) turbulent flame is injected into the main chamber. The objective of this research is to examine those effects upon the combustion characteristics and the burned gas composition. The characteristics of flame propagation were examined by using a series of schlieren photographs. A summary of the major conclusion of this research is given below: (1) The mixtures supplied in the main and the auxiliary chambers burn without mixing with each other. (2) The concentrations of HC and CO decrease as the closer the mixture in the auxiliary chamber approaches stoichiometry and the leaner the mixture in the main chamber. The concentration of CO decreases as the torch opening area decreases. (3) The concentration of NOx decreases as the mixture in the auxiliary chamber becomes richer, the mixture in the main chamber becomes leaner and the torch opening area becomes larger.
Furukawa, Junichi, Mizumura, Sakae, Yoshida, Masatake, Gomi, Tsutomu
Current Developments in Spark-Ignition Engines7606062/1/1976
This paper reviews the major changes that have occurred in spark-ignition engine design and operation over the last two decades. The automobile air pollution problem, automobile emission standards, and automobile fuel economy standards -- the factors which have and are producing these changes -- are briefly described. The major components in spark-ignition engine emission control systems are outlined, and advances in carburetion, fuel injection, ignition systems, spark retard and exhaust gas recycle strategies, and catalytic converters, are reviewed. The impact of these emission controls on vehicle fuel economy is assessed. The potential for fuel economy improvements in conventional spark-ignition engines is examined, and promising developments in improved engine and vehicle matching are outlined. Finally, the operating characteristics of alternative spark-ignition engines - the Wankel and several stratified charge engines -- which are competing with the conventional engine, are briefly discussed.
Heywood, John B., Tabaczyniski, Rodney J.
Performance of Methanol-Gasoline Blends in a Stratified Charge Engine Vehicle7605462/1/1976
A series of driveability and chassis dynamometer tests were performed using various blends of methanol and gasoline in a stratified charge engine vehicle. The vehicle used was a 1975 Honda Civic CVCC. This vehicle is powered by a prechamber type stratified charge spark ignition engine. The basic intent of this effort was to characterize how methanol-gasoline blends behave in a prechamber stratified charge engine vehicle. Since the stratified charge engine was designed to operate at overall lean air fuel ratios, the leaning effect of methanol blended with gasoline might not produce the general degradation of vehicle performance, emissions, and fuel economy reported for late model vehicles. The test program was separated into two phases. The first phase was to determine the effect of methanol-gasoline blends on the drive-ability of the stratified charge engine vehicle. Blends containing 10% to 40% by volume of methanol in gasoline were tested. A weighted demerit system was used to evaluate driveability. Based on this system, vehicle driveability improved slightly with a 10% by volume blend of methanol in gasoline. A 15% by volume blend of methanol yielded vehicle driveability roughly comparable to the base gasoline alone. Further increases in the methanol content produced increased degradation of the driveability. The vehicle would operate on the 40% by volume blend but it was essentially undriveable. Cold weather tests using winter grade gasoline as a base fuel demonstrated that 10% methanol had approximately the same effect on driveability for winter grade fuels as for summer grade fuels. Emissions and fuel economy of the vehicle operating on base fuels and base fuels blended with methanol were evaluated using a chassis dynamometer and the federal urban driving schedule. The addition of 10% methanol to the base fuels produced only very minor changes in the emissions and fuel economy of the vehicle. Not all indicated changes were statistically significant. Generally, HC emissions increased, CO emissions decreased slightly, NOx emissions decreased, and volumetric fuel economy decreased slightly. General conclusions are that the CVCC vehicle tested suffered only slight degradation in driveability using a 10% methanol-gasoline fuel and vehicle emissions and fuel economy are not significantly changed by use of the 10% methanol blend.
Johnson, R. T., Riley, R. K., Dalen, M. D.
Performance Characteristics of Stratified Charge Vehicles with Conventional Fuels and Gasoline Blended with Alcohol and Water7601972/1/1976
The effects of fuel volatility and alcohol content on vehicular performance were determined in unmodified conventional, prechamber stratified charge, and direct injection open-chamber stratified charge vehicles. A clear water-gasoline emulsion fuel was included in the test sequence. Driveability testing revealed that the stratified charge powered vehicles were relatively insensitive to base fuel volatility. Driveability depreciated with increasing alcohol content for all vehicles. Testing of the water-gasoline emulsion showed driveability was unsatisfactory in vehicles powered with conventional and prechamber stratified charge engines but marginally acceptable in the open-chamber stratified charge engine. Increasing alcohol content up to 20 V % increased mass emissions of the open-chamber stratified charge engine, reduced emissions of the prechamber stratified charge engine, and had no significant effect on the conventional engine. Fuel economy on an energy utilization basis was improved with increasing alcohol content and reduced with the water-gasoline emulsion.
Boekhaus, K. L., Copeland, L. C.
Performance and NOx Emissions Modeling of a Jet Ignition Prechamber Stratified Charge Engine7601612/1/1976
The development of a cycle simulation model for the jet ignition prechamber stratified charge engine is described. Given the engine geometry, load, speed, air-fuel ratios and pressures and temperatures in the two intakes, flow ratio and a suitable combustion model, the cycle simulation predicts engine indicated efficiency and NO emissions. The relative importance of the parameters required to define the combustion model are then determined, and values for ignition delay and burn angle are obtained by matching predicted and measured pressure-time curves. The variation in combustion parameters with engine operating variables is then examined. Predicted and measured NO emissions are compared, and found to be in reasonable agreement over a wide range of engine operation. The relative contribution of the prechamber NO to total exhaust NO is then examined, and in the absence of EGR, found to be the major source of NO for overall air-fuel ratios leaner than 22:1.
Hires, S. D., Ekchian, A., Heywood, John B., Tabaczynski, R. J., Wall, J. C.
Fuel Consumption in European Passenger Cars Powered by Gasoline, Diesel, and Direct Injection Stratified Charge Engines7607962/1/1976
A comparison has been made between the fuel consumption of a typical European passenger vehicle powered by gasoline, Diesel and Stratified Charge Engines having performance characteristics allowing equal vehicle acceleration. The study shows that on the average the gasoline and Diesel fuel consumption are similar, while with the S.C.E. a benefit of from 7-20% was observed. Compliance with the European regulations is the main exhaust emission constraint within the study that has been conducted. But, when available, exhaust emissions data for the U.S.E.P.A. “FTP” cycle have also been quoted.
Ciccarone, A., Antonini, C., Virgilio, U.
Stratified Charge Engines7607552/1/1976
The objectives of this project were to determine the acceptability of various types of stratified charge engines as potential power plants for light duty vehicles and motorcycles in America. The light duty vehicle considered was a four/five seat compact sedan with good acceleration capabilities and exhaust emissions below a primary target of 0.41 g/mile HC, 3.4 g/mile CO, 1.5 g/mile NOx. A secondary target of 0.41 g/mile HC, 3.4 g/mile CO and 0.4 g/mile NOx was also considered. A literature survey was undertaken, comparing stratified charge engines with examples of good conventional gasoline and diesel engines. While some stratified charge engines had exhaust emission or fuel economy advantages, there were always sacrifices in other areas. Eleven engines were configured, four of which were specifically directed towards the secondary emission targets. A method of rating the engines was derived, and the design concepts were compared with two gasoline engines by a jury panel. The overall result was that the Ford PROCO and Honda CVCC combustion processes were serious contenders to the gasoline engine at the primary emission target, and that both of these systems, together with the VW combustion process, might be suitable at the secondary targets.
Haslett, R. A., Monaghan, M. L., McFadden, J. J.
The Texaco Ignition System-A New Concept for Automotive Engines7503472/1/1975
The Texaco Ignition System (TTIS) is a high frequency system with a bi-directional spark current, the duration of which is a function of crankshaft rotation rather than time. The spark current characteristics differ drastically from those of conventional discharge systems and, as a result, current flow through the plug gap can be maintained under extremely turbulent conditions. Being essentially a constant current device, it prevents excessive plug current flow during initial gap ionization, providing a good plug life; yet it has high average current to increase fuel ignition probability. The system, developed primarily for use with stratified charge engines, has also been shown to have characteristics which improve the performance of premixed charge engines operated under severe conditions, in order to reduce exhaust emissions, improve driveability and increase fuel economy. TTIS is of solid state design, and both the spark timing and spark duration are controlled by use of digital logic circuitry.
Canup, R. E.
A Progress Report on Curtiss-Wright's Rotary Stratified Charge Engine Development7412062/1/1974
Development progress of the direct injected Stratified Charge Rotary engine program at Curtiss-Wright is detailed. Basic configurations are described and compared to both reciprocating stratified charge engines and the carbureted Rotary engine. Data and theoretical analyses are presented for progressive developments from initial feasibility testing in 1962 through current configurations now on test. It is concluded that the Stratified Charge Rotary Engine research efforts to date have demonstrated potential for an efficient, lightweight, compact, economic powerplant capable of broad range operations justifying further research efforts.
Jones, Charles
Single-Cylinder Study of Stratified Charge Process with Prechamber-Injection7411622/1/1974
The purpose of this paper is to contribute to knowledge of the behavior of the stratified charge engine with prechamber injection by experimental investigation of several important parameters. Special attention is given to degree of charge stratification, position of injection nozzle and spark plug in the prechamber, construction of the injection nozzle, start of injection, timing of ignition, and throttling of the intake air. These parameters have a more or less significant influence on output, fuel consumption, and exhaust emission. Finally, the combustion system was adjusted partly by optimizing and partly by compromising. Comparison with a conventional spark ignition engine is made. Using a mathematical model of the process, the possible causes of the significant improvements in NO emissions are discussed.
Pischinger, F. F., Klöcker, K. J.
A Two-Charge Engine Concept: Hydrogen Enrichment *7411692/1/1974
The first engine dynamometer test results are presented for a modified fuel system based on hydrogen enrichment for a V-8 I.C. engine. The engine burns mixtures of gasoline and hydrogen under ultralean conditions to yield extreme low NOx emissions with increased engine efficiency. The hydrogen is produced in a compact onboard generator from gasoline and air. The hydrogen-rich product gas is cooled and mixed with the normal combustion air in a modified carburetor. The engine then operates in the conventional manner on atomized gasoline with spark ignition, but with hydrogen-enriched air and with a high spark advance of 40-50° BTDC. The engine thus receives two charges of fuel: a charge of gaseous fuel from the hydrogen generator, and the normal gasoline charge. The results on hydrogen enrichment are compared with the 1973 V-8 baseline stock engine with emission controls, and the same engine without controls and operated at a maximum efficiency under lean conditions. All results are compared at level road load as a function of rpm. Relative to the stock 1973 350 CID engine, an approximate 10 percent reduction in brake specific fuel consumption was measured over the entire level road load speed range. For the same condition, NOx emissions were reduced to below the equivalent 1977 EPA Standards (0.4 gm/mi). Further effort is required to reduce the remaining two exhaust pollutants to the corresponding level, i.e. 0.41 gm/mi HC and 3.4 gm/mi CO. The hydrogen enrichment concept is compared with a pre-chamber stratified charge engine. The analogy is made that if the pre-chambers for each cylinder were combined into a single pre-combustor, it shows some similarities to the hydrogen generator.
Houseman, John, Hoehn, Frank W.
A Search for a Low Nitric Oxide Engine7411722/1/1974
Various homogeneous charge and stratified charge engine configurations were studied at wide-open throttle conditions, using simplified computer models. An order-of-magnitude parametric study was performed to find those combinations of variables which predicted a low nitric oxide level. Extreme values of variables were studied for a homogeneous charge engine configuration, which could be difficult to do in a real engine. As expected, these calculations indicated that for practical engine operation the equivalence ratio of the mixture must either be very rich or very lean for a resultant low nitric oxide level. Two extremes of stratified charge engine operation were investigated analytically, in other words, immediate mixing of newly formed products of rich combustion with excess air (instantaneous mixing) and a period of rich combustion followed by air addition to the rich products (delayed mixing). Comparisons of power, efficiency, and specific NOx are presented. For a low level of specific NOx the acceptable engine configurations are very rich homogeneous combustion, very lean homogeneous combustion, overall lean instantaneous mixing stratified charge and overall stoichiometric delayed mixing stratified charge.
Evers, L. W., Myers, P. S., Uyehara, O. A.
VEHICLE EMISSION SYSTEMS UTILIZING A STRATIFIED CHARGE ENGINE7411572/1/1974
Vehicle systems utilizing a stratified charge engine have been evaluated for their emission potential. They have shown the ability to meet the 2.0 gm/mi NOx emission standard without EGR at low mileage, but require some form of aftertreatment device to simultaneously achieve emission levels of 0.41 gm/mi HC and 3.4 gm/mi CO. The system hardware required in conjunction with the stratified charge engine is described.
JOHNSON, P. R., GENSLAK, S. L., NICHOLSON, R. C.
Pre-Chamber Stratified Charge Engine Combustion Studies7411592/1/1974
Single-cylinder experiments were conducted with a 3-valve carbureted pre-chamber stratified charge engine in comparison with a conventional engine. The pre-chamber engine operation is governed by many design and operating variables. This investigation was limited to determining the effect of overall air/fuel ratio, ignition timing and EGR on emissions and fuel economy at a single road load test condition. It was found that, as for the conventional engine, these operating variables are also significant for the pre-chamber engine and that a compromise must be made between good fuel economy and low emissions. The main virtue of the pre-chamber engine was found to be the ability to operate at leaner overall air-fuel ratio. This resulted in lower nitrogen oxide (NO) emissions than the conventional engine without EGR. The unburned hydrocarbons (HC) were found to be higher for the pre-chamber engine up to the conventional engine lean misfire A/F ratio. Exhaust gas introduced into the pre-chamber was found to reduce NO emissions significantly without a large corresponding increase in HC emissions as observed with the conventional engine. Only at very low NO emissions with severely with severely retarded spark timing and/or high EGR rate did the pre-chamber engine show a fuel economy advantage over the conventional engine. As the test program was limited to one load and speed, the results should not be construed to be typical of all modes of operation.
Purins, Egils A.
Texaco's Stratified Charge Engine - Multifuel Efficient, Clean, and Practical7405632/1/1974
This paper reports on the continuing development of Texaco's stratified charge engine combustion concept, the Texaco Controlled-Combustion System. TCCS conversions of the military L-141 engine have demonstrated inherently low exhaust emissions, multifuel capability, and improved fuel economy over the carburetted L-141 gasoline engine. Under contract to the U.S. Army Tank-Automotive Command, promulgated federal gaseous exhaust emissions standards were met in a naturally aspirated TCCS engine-powered M-151 vehicle equipped with EGR- and Texaco-developed exhaust catalysts. These low emissions were sustained for 50,000 miles (80,400 km) with moderate maintenance. The effects of different degrees of emission control and of multifuel operation on performance and fuel economy were characterized using a turbocharged L-141 TCCS engine-powered M-151 vehicle.
Alperstein, M., Schafer, G. H., Villforth, F. J.
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