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At high load, dual-fuel compression ignition engines often rely on exhaust gas recirculation (EGR) to avoid excessive in-cylinder pressure rise rates caused by the autoignition of the premixed fuel. This can adversely affect the net indicated efficiency depending on the resulting fuel/air equivalence ratio and pressure differential across the cylinder used to drive the requested amounts of EGR. In this work, advanced combustion control strategies have been experimentally investigated to improve ethanol-diesel dual-fuel operation at a high engine load of 1.8 MPa net indicated mean effective pressure. Miller cycle and charge air cooling have been explored to reduce the in-cylinder gas temperature and help control the ethanol autoignition process, potentially minimising the EGR requirements and increasing net indicated efficiency. Experiments were carried out on a single-cylinder heavy-duty engine equipped with a high pressure common rail diesel injection, an ethanol port fuel injection, and a variable valve actuation system on the intake camshaft. Exhaust emissions and net indicated efficiency were measured and discussed for different ethanol energy fractions. Early autoignition of the premixed ethanol fuel at the baseline intake valve lift profile resulted in high levels of pressure rise rate, which limited the ethanol energy fraction to 0.26. The application of a Miller cycle strategy via late intake valve closing events effectively delayed the ethanol autoignition process. The reduction of the intake manifold air temperature via an air-to-water charge air cooler also suppressed the early ignition of ethanol. Both approaches allowed for a substantial improvement in terms of the maximum ethanol energy fraction, which was increased to 0.79 without EGR. Moreover, high load dual-fuel operations with Miller cycle and charge air cooling attained higher net indicated efficiency and lower nitrogen oxides emissions than conventional diesel combustion. These improvements can help generate a viable business case of dual-fuel combustion as a technology for future compression ignition engines. [ABSTRACT FROM AUTHOR]

The upcoming emission legislation for sea-going vessels issued by the international marine organization requires drastic reduction in nitric oxides. A well-known approach for meeting these requirements is to reduce the in-cylinder temperature prior to combustion by using the so-called Miller cycle. However, the mere use of this technique presents the actual limits due to long ignition delay, which occurs when the compression temperature is very low. As a consequence, premixed combustion develops quickly, increasing the local temperature in the combustion chamber and favoring NOx formation. Splitting the fuel injection into a small pilot and a main injection can reduce the magnitude of the premixed combustion and the local in-cylinder temperatures. The work presented here is divided in two parts and is novel by being the first systematic study of split injection combined with Miller cycle in large-bore engines. In its first stage, an extensive study of the injection dwell with two intake valve closings and three timings of the main injection are analyzed. In the second stage, both injection events are shifted later in the power stroke with fixed injection dwell. Overall, the pilot injection reduced the ignition delay but dropped the peak of the premixed combustion only with the most advanced intake valve closing. This improved fuel economy, but provided no advantages as far as emissions are concerned. In addition, while increasing injection dwell reduced NOx emissions, it also increased fuel consumption. The highest achieved NOx reduction was close to 60%, with a small drawback in fuel economy. [ABSTRACT FROM AUTHOR]

Pollutant exhaust emissions, particularly NOx, produced by diesel engines must be reduced to limit values defined by the environmental regulations as the emissions have many harmful influences on the environment. Recently, the application of the Miller cycle into the internal combustion engines has been proposed to abate NOx emissions. In the present study, the Miller cycle with late intake valve closing (LIVC) version is applied into a single cylinder, four-stroke, direct injection, naturally aspirated diesel engine. Three different cam shafts have been manufactured to provide 5, 10 and 15 crank angle (CA) retarding compared to original camshaft. The optimum retarding angle has been determined as 5 CA in terms of NOx reduction. The attained results have been compared with conventional diesel engine which has standard CA (0 crank angle retarding) in point of the performance and NO, HC, CO emissions. In order to provide a model validation for engine torque, brake power, brake efficiency, specific fuel consumption (SFC) and NO, the Miller cycle diesel engine is modeled by using two-zone combustion model for 5 CA retarding at full load conditions. The simulation results have been verified with experimental data with non-considerable errors. In the experimental results, NO emissions decreased by 30% with 2.5% power loss and a remarkable change is not seen in the HC, CO emissions. The results show that the method could be easily applied into the diesel engine in order to minimize NO emissions. [ABSTRACT FROM AUTHOR]

Highlights: [•] Paper explores the potential of the Miller cycle, applied to HSDI Diesel engines. [•] The benefit is the reduction of combustion temperature and NOx emissions. [•] The goal of the study is to assess the potential and the limits of this technique. [•] A 2.8L engine was selected, CFD tools have been calibrated through experiments. [•] CFD simulations shows a reduction of NOx and Soot of 25 and 60%. [ABSTRACT FROM AUTHOR]

Abstract: This paper presents an investigation into the feasibility and potential advantages of a small scale Miller cycle natural gas engine for applications such as domestic combined heat and power systems. The Miller cycle engine is compared to a standard Otto cycle engine using cycle analyses and multidimensional simulation, and basic engine design implications are discussed. It is found that the Miller cycle engine has a potential for improved fuel efficiency, but at the cost of a reduced power to weight ratio. A fuel efficiency advantage of compared to a standard Otto cycle engine appears possible, however it is stated that further investigations, in particular into the topic of engine friction, are required in order to validate the findings. [Copyright &y& Elsevier]

Abstract: A conceptual analysis of the mechanism of the Miller cycle for reducing NO x emissions is presented. Two versions of selected Miller cycle (1 and 2) were designed and realized on a Rover “K” series 16-valve twin-camshaft petrol engine. The test results showed that the application of the Miller cycle could reduce the NO x emissions from the petrol engine. For Miller cycle 1, the least reduction rate of NO x emission was 8% with an engine-power-loss of 1% at the engine’s full-load, compared with that of standard Otto cycle. For Miller cycle 2, the least reduction rate of NO x emission was 46% with an engine-power-loss of 13% at the engine’s full-load, compared with that of standard Otto cycle. [Copyright &y& Elsevier]

Abstract: Using finite-time thermodynamics, the relations between thermal efficiency, compression and expansion ratios for an ideal naturally-aspirated (air-standard) Miller cycle have been derived. The effect of the temperature-dependent specific heat of the working fluid on the irreversible cycle performance is significant. The conclusions of this investigation are of importance when considering the designs of actual Miller-engines. [Copyright &y& Elsevier]