Search Results

One of the main challenges with the Homogeneous Charge Compression Ignition, HCCI, combustion system is to control the Start Of Combustion, SOC, for varying load and external conditions. A method to achieve this on a cycle-by-cycle basis is to vary the valve timing based on a feedback signal from the SOC of previous cycles. The control can be achieved with two basic valve-timing strategies named the Overlap- and the IVC-method. The Overlap-method works by trapping of residuals while the IVC-method affects the effective compression ratio. In an earlier paper it has been shown that if the two methods are incorporated into one controller, SOC can be controlled in a relatively large operating window although the transient performance was not sufficient. The reason is that the simple PI-controller cannot be made fast enough to cope with the transients without magnifying the cycle-to-cycle variations of the combustion into instability.

The diesel engine is still one of the most common and most efficient mobile energy converters. Nevertheless, it is troubled by many problems, one of them being nozzle coking. This is not a new problem; however, due to the introduction of more advanced injection systems and a more diverse fuel matrix, including biofuels, the problem has become more complex. The nozzle holes are also much narrower today than when the problem first appeared and are therefore more sensitive to coking. Two CEC sanctioned coking tests exist for diesel engines, but no universally accepted test for heavy duty engines. In this paper, tests have been performed with B10 doped with 1 ppm zinc on a single cylinder engine, based on a heavy duty engine, with the purpose to develop a simple accelerated coking test. To have relevance to real usage, the test was based on real engine load points from a high power Euro V engine calibration. The coking propensity was studied in an engine speed sweep at max load.

Homogeneous Charge Compression Ignition, HCCI, has the attractive feature of low particulate and low NOx emission combined with high efficiency. The principle is a combination of an Otto and a Diesel engine in that a premixed charge is ignited by the compression heat. One of the main challenges with the HCCI combustion system is to control the combustion timing/phasing for varying load and external conditions. A method to achieve this on a cycle-by-cycle basis is to vary the valve timing based on a feedback signal from the combustion timing of previous cycles. A combined engine and control simulation is performed. The simulations are accomplished with a commercial cycle simulation code linked with a commercial control simulation code. The simulations are iteratively verified against engine test data. Engine tests are conducted on a single cylinder engine equipped with at hydraulic valve system that allows a high degree of freedom in choosing the valve timings.

Nozzle coking in diesel engines has received a lot of attention in recent years. High temperature in the nozzle tip is one of the key factors known to accelerate this process. In premixed CNG-diesel dual fuel, DDF, engines a large portion of the diesel fuel through the injector is removed compared to regular diesel operation. This can result in very high nozzle temperatures. Nozzle hole coking can therefore be expected to pose a significant challenge for DDF operation. In this paper an experimental study of nozzle coking has been performed on a DDF single cylinder engine. The objective was to investigate how the rate of injector nozzle hole coking during DDF operation compares to diesel operation. In addition to the nozzle tip temperature, the impact of other parameters on coking rate was also of interest. Start of injection, λ, diesel substitution ratio and common rail pressure were varied in two levels starting from a common baseline case, resulting in a total of 10 operating cases.

In previous studies it has been shown that the auto-ignition quality of a fuel at a given engine condition can be described by an octane index defined as, OI=(1-K) RON + K MON, where RON and MON characterize the fuel and the K-value depends only on the engine design and operating conditions. It has been shown that the K-value is highly dependent on the pressure and temperature history. Another important parameter is OI0, the OI of the fuel which gives heat release centred at top dead center; OI0 can be considered to be the requirement of the engine. In previous work, empirical relations for both K and OI0 in terms of in-cylinder pressure and temperature and engine speed and mixture strength were found but the influence of EGR was not considered.

In order for premixed methane diesel dual fuel engines to meet current and future legislation, the emissions of unburned hydrocarbons must be reduced while high efficiency and high methane utilization is maintained. This paper presents an experimental investigation into the effects of in cylinder air motion, swirl and tumble, on the emissions, heat transfer and combustion characteristics of dual fuel combustion at different air excess ratios. Measurements have been carried out on a single cylinder engine equipped with a fully variable valve train, Lotus AVT. By applying different valve lift profiles for the intake valves, the swirl was varied between 0.5 and 6.5 at BDC and the tumble between 0.5 and 4 at BDC. A commercial 1D engine simulation tool was used to calculate swirl number and tumble for the different valve profiles. Input data for the simulation software was generated using a steady-state flow rig with honeycomb torque measurements.

One of the main challenges with the Homogeneous Charge Compression Ignition, HCCI, combustion system is to control the Start Of Combustion, SOC, for varying load and external conditions. A method to achieve this on a cycle-by-cycle basis is to vary the valve timing based on a feedback signal from the SOC of previous cycles. The control can be achieved with two basic valve-timing strategies named the Overlap- and the IVC-method. The Overlap-method works by trapping of residuals while the IVC-method affects the effective compression ratio. In an earlier paper it has been shown that if the two methods are incorporated into one controller, SOC can be controlled in a relatively large operating window although the transient performance was not sufficient. The reason is that a simple PI-controller cannot be made fast enough to cope with the transients without magnifying the cycle-to-cycle variations of the combustion into instability.

Homogeneous Charge Compression Ignition, HCCI, has the attractive feature of low particulate emission and low Nitrogen Oxides, NOx, emission combined with high efficiency. The principle is a combination of an Otto and a Diesel engine in that a premixed charge is ignited by the compression heat. One of the main challenges with the HCCI combustion system is to control the Start Of Combustion, SOC, for varying load and external conditions. A method to achieve this on a cycle-by-cycle basis is to vary the valve timing based on a feedback signal from the SOC of previous cycles. The control can be achieved with two basic valve-timing strategies, named the Overlap- and the IVC-method. The Overlap-method works by trapping of residuals while the IVC-method affects the effective compression ratio. These methods have in an earlier paper been verified to work one at a time to control SOC during engine transients [1].