The Achates Power Inc. (API) Opposed Piston (OP) Engine architecture provides fundamental advantages that increase thermal efficiency over current poppet valve 4 stroke engines. In this paper, combustion performance of diesel and gasoline compression ignition (GCI) combustion in a medium duty, OP engine are shown. By using GCI, NO x and/or soot reductions can be seen compared to diesel combustion at similar or increased thermal efficiencies. The results also show that high combustion efficiency can be achieved with GCI combustion with acceptable noise and stability over the same load range as diesel combustion in an OP engine.

Two-stroke engines are capable of providing very high power density levels in a cost effective, easy-to-maintain package. They are, however, typically susceptible to higher levels of hydrocarbon emissions, lower durability, and a shorter lifecycle when compared to four-stroke engines. These detriments are easily overlooked in some military applications where power density is paramount, but most commercial two-stroke engines require specialized consumable lubricant. Typical military applications strive to minimize their logistics “trails,” which includes minimizing the variety of fluids they require. As a result, there has been very limited success in fielding small two-stroke engines for military use. As a preliminary study, MIL-PRF-2104K Single Common Powertrain Lubricant (SCPL, a four-stroke heavy diesel engine oil) was utilized as the consumable lubricant (in place of conventional two-stroke oil) in a liquid-cooled, semi-direct fuel injected, spark-ignition, two-stroke engine. Empirical data was collected to study the impact of the oil on deposit build-up, power, wear, combustion stability, and fuel conversion efficiency. Over 147 hours of operation were logged and analyzed. The performance of the engine on SCPL was consistent with conventional two-stroke oil and showed no degradation over the test duration. Brake specific fuel consumption was not negatively impacted with SCPL. Increased deposit build-up in the exhaust ports and on the spark plugs were the primary negative impacts of the SCPL oil. Spark plugs with hotter classifications and modification of the oiling rate resulted in a reduction of soot accumulation and spark plug fouling.

This paper discusses chemical kinetic modeling used to analyze the formation of pollutant emissions in large-bore, lean-burn gas reciprocating engines. Pollutants considered are NOx, CO, HCHO, and UHC. A quasi-dimensional model, built as a chemical reactor network (CRN), is described. In this model, the flame front is treated as a perfectly stirred reactor (PSR) followed by a plug flow reactor (PFR), and reaction in the burnt gas is modeled assuming a batch reactor of constant-pressure and fixed-mass for each crank angle increment. The model treats full chemical kinetics. Engine heat loss is treated by incorporating the Woschni model into the CRN. The mass burn rate is selected so that the modeled cylinder pressure matches the experiment pressure trace. Originally, the model was developed for large, low speed, two-stoke, lean-burn engines. However, recently, the model has been formatted for the four-stroke, open-chamber, lean-burn engine. The focus of this paper is the application of the model to a four-stroke engine. This is a single-cylinder non-production variant of a heavy duty lean-burn engine of about 5 liters cylinder displacement Engine speed is 1500 RPM. Key findings of this work are the following. 1) Modeled NOx and CO are found to agree closely with emission measurements for this engine over a range of relative air-fuel ratios tested. 2) This modeling shows the importance of including N 2 O chemistry in the NOx calculation. For λ = 1.7, the model indicates that about 30% of the NOx emitted is formed by the N 2 O mechanism, with the balance from the Zeldovich mechanism. 3) The modeling shows that the CO and HCHO emissions arise from partial oxidation late in the expansion stroke as unburned charge remaining mixes into the burnt gas. 4) Model generated plots of HCHO versus CH 4 emission for the four-stroke engine are in agreement with field data for large-bore, lean-burn, gas reciprocating engines. Also, recent engine tests show the correlation of UHC and CO emissions to crevice volume. These tests suggest that HCHO emissions also are affected by crevice flows through partial oxidation of UHC late in the expansion stroke.

Generally, two-stroke engines have inherent advantage of higher swirl, as compared to four-stroke engines. Higher swirl helps with better mixing and atomization for mechanical and low pressure, electronic, unit injectors. With the introduction of higher injection pressure, the advantage of swirl reduced to a point in which it started to have a negative impact. In this work, the goal was to optimize a high pressure, common rail injection system for heavy-duty, two-cycle, medium speed, diesel engine (710 cubic inches of displacement per cylinder) under high load. A proprietary multi-dimensional computational fluid dynamic (CFD) code was used for the modeling work. Here, we optimized the new, skewed injection system, which takes advantage of swirl and further helps in atomization of spray. The spray in this study is introduced at a radial angle, which is aligned either along or against the swirl direction. The results showed significant improvement in combustion efficiency. Combustion efficiency is estimated as a decrease in fuel consumption and CO values. Emission parameters, such as nitrogen oxide and soot were also studied and showed significant reductions.

Traditionally, torsional vibration analysis (TVA) programs operating in frequency domain, consider only one 2- or 4-stroke engine cycle to simulate a steady-state dynamics of the powertrain. There are, however, some phenomena which cannot be revealed during a single-cycle simulation. First such case is related to propeller drives. If the transmission ratio between internal combustion engine and propeller shaft is not synchronized with the number of propeller blades, then low-frequency fluctuations of vibration magnitude (beats) are induced, which can only be seen if multiple engine cycles are analyzed. Second case refers to simulation of random misfiring. Although an isolated event, it has an influence on the system dynamics beyond the engine cycle where it happens, and therefore requires considering multiple cycles. The paper shows how these two cases are dealt with, using AVL software EXCITE Designer.

Modern, high-performance, outboard marine engines operate in severe environments. They are typically mounted to a planing boat operating at high horsepower levels due to high hydrodynamic drag. The engine also experiences high vertical impact loads in rough-water conditions. In the ocean, corrosive salt water circulates through the engine to provide necessary engine cooling. Splashing water can be ingested into the combustion air inlets on the outside of the engine cowl (engine enclosure) and must be appropriately managed. In addition, the engine often operates in very warm climates with a sealed cowl wrapped tightly around it. The warm atmospheric air that flows through the cowl inlets and into the engine compartment must first circulate around the power head in order to cool thermally sensitive components such as engine controllers and ignition coils. In some applications, the same air stream mixes with fuel then participates in the combustion process inside the cylinder. At Mercury Marine, computational fluid dynamics, CFD, is used to aid the design of outboard engines that will operate robustly in these extreme conditions. One specific application for CFD is the management of the flow and thermal aspects of engine-compartment air flow. Studies can be done with CFD to assist product design decisions that aim to balance the need to protect thermally sensitive electronics and to efficiently provide the engine with the combustion air. The CFD simulation predicts the air flow behavior from the cowl duct inlets, around the power-head, and into the throttle body inlet of the engine. The simulation also predicts air temperatures, component temperatures, and heat flow to and from the air. The CFD model typically includes rotating components such as alternators and flywheels. A recent study was conducted to validate the CFD method. The CFD model and the dynamometer experiments were conducted with a mid-size outboard 4-stroke engine. The test engine was fully instrumented to measure air temperatures, air velocities, and component temperatures. The validation exercise included a detailed comparison of these values between the CFD predictions and the experimental results. A high level of agreement was achieved and a few lessons were captured for future implementation.

The tailpipe emissions from automotive engines have been subject to steadily reducing legislative limits. This reduction has been achieved through the addition of sub-systems to the basic four-stroke engine which thereby increases its complexity. To ensure the entire system functions correctly, each system and / or sub-systems needs to be continuously monitored for the presence of any faults or malfunctions. This is a requirement detailed within the On-Board Diagnostic (OBD) legislation. To date, a physical model approach has been adopted by the automotive industry for the monitoring requirement of OBD legislation. However, this approach has restrictions from the available knowledge base and computational load required. A neural network technique incorporating Multivariant Statistical Process Control (MSPC) has been proposed as an alternative method of building interrelationships between the measured variables and monitoring the correct operation of the engine. Building upon earlier work for steady state fault detection, this paper details the use of non-linear models based on an Auto-associate Neural Network (ANN) for fault detection under transient engine operation. The theory and use of the technique is shown in this paper with the application to the detection of air leaks within the inlet manifold system of a modern gasoline engine whilst operated on a pseudo-drive cycle.

Common rail injection is not a new idea. For example Sulzer was running tests with a mechanical common rail system as early as 1915. Also the idea of an electronically controlled injection system is more than three decades old. At the moment common rail injection is state of the art for trucks and diesel passenger cars.

In two-stroke engines replacement of carburetors with direct fuel injection systems greatly reduces engine emissions and fuel consumption by eliminating fuel short-circuiting. Air-blast direct fuel injection using a dedicated air pump has been successfully applied to both two- and four-stroke engines. In this study we re-examine the design of a low cost compression pressurized direct injection system. This system uses gases extracted from the combustion chamber during the compression stroke to supply pressure for the air blast injection, thus eliminating the air pump [1,2]. Gases, predominantly scavenging air, are transferred to a mixing cavity from the combustion chamber via a small (5mm diameter) solenoid poppet valve as the piston rises during the compression stroke. Proper functioning of the system requires careful optimization of the mixing cavity size and the blast valve timing to ensure adequate mixing cavity pressure and fuel atomization. To assist in the optimization of these design parameters a one-dimensional fluid dynamics model has been developed. Parameter sensitivity studies were carried out using the model to determine the optimum cavity size, blast valve timing, and fuel injection duration. These parameters were optimized over a wide range of engine speeds and throttle settings. Results show that a mixing cavity pressure of 500 kPa is attainable over the range of 1000 to 6000 rpm, from closed throttle to wide open throttle (WOT) without cavity pressurization encroaching into the ignition regime. Fuel maps and valve timings are presented and results are contrasted with the carbureted case, showing improved fuel efficiency and emissions for the direct injection system. These data will be used in the design of a physical demonstration engine.

The reduction of friction in the valve train of four-stroke combustion engines is a promising opportunity to decrease fuel consumption and to improve pollutant emissions. The possibilities are reviewed by comparing light weight and newly developed components. The friction in the valve train causes a loss from the BMEP by about 0.2 to 0.4 bar. To measure friction forces in this range requires constant and well maintained environmental conditions. The viscosity as well as the pressure and temperature of the lubricating oil have a big influence on the friction. Due to the valve spring forces a strong fluctuation of the cam torque appears. This makes it very demanding to set up the measurement equipment in a correct way. Measurement equipment which is able to gauge with sufficient accuracy may be overloaded by the effects caused by the spring forces. Based on this special care is necessary during the first ramp up of the cylinder head. It has to be modified to avoid overloading the measurement equipment. One possibility to achieve lower friction between the valve stem and the valve guide is the reduction of the lateral forces which are caused by the asymmetry of the valve spring. Using recently new developed components these detrimental forces within a valve train can be reduced which leads to lower friction losses. In addition the wear between the valve train components can be reduced. In detail this can be accomplished by using two-piece spring retainer which allows a tilted position of the spring end during the valve lift and by this only allow axial forces to act onto the valve. The friction in a valve train using a direct acting mechanical tappet is mainly caused by the sliding contact of the cam on the tappet face. To lower the friction in this area the spring forces have to be reduced. This requires valve train components with lower masses and weaker springs. Therefore valves, spring retainers and tappets made from light weight alloys where developed. The mass of these light weight components could be reduced by more than 50%. Detailed measurements are performed and the results will be presented. As a conclusion it can be seen, what light weight components in the valve train of four stroke engines can contribute to a torque reduction in innovative valve trains.

In four-stroke engines direct injection increases power and fuel economy, which is further improved by charge stratification, due to pumping loss reduction and better combustion efficiency at partial loads. Charge stratification can be obtained by different techniques and injector designs. In every case late injection is necessary for stratification, which however is impaired by fuel dilution and spreading in consequence of burnt gas expansion, leading to incomplete combustion at very light loads. A numerical study has been carried out modifying KIVA code to handle new piston shapes. An innovative combustion chamber that is split in two volumes and allows fuel confinement during combustion has been conceived. CFD comparison has been made between a conventional combustion chamber and the proposed new one in term of combustion efficiency. Combustion is enhanced by the new design and unburnt emissions are reduced.