In 1996, Volkswagen was the first to develop a passenger diesel engine with an undivided combustion chamber (“direct injection”) on the third-generation Golf. The advantages of such motors compared to the pre-chamber are difficult to overestimate. This is a high efficiency of the combustion process and the corresponding efficiency, great potential for boosting the engine and the best environmental performance. The passivity is the “rigidity” of the work that they learned to win, and the high requirements for fuel equipment.
Previously, such motors were used mainly on trucks. There, efficiency and excellent specific indicators have long allowed us to close our eyes to a little more noise and vibration. On cars of the 80s, pre-chamber diesel engines dominated, working noticeably softer.
The nozzles of complex design provided a “direct” diesel engine with two-phase injection. The main dose of fuel was preceded by the so-called pilot. So it was possible to reduce the evaporation of fuel in the combustion chamber during the delay period of self-ignition. The engine began to work softer. However, two-phase injection was only a temporary solution. Further, the paths were divided - some manufacturers, led by Volkswagen, chose pump nozzles, relying on high injection pressure and accurate dosing. The rest chose a system with a “cumul rail” storage line, where with slightly lower pressure there are more injection control options.
Today, a system with a common line is ready to fight on equal terms with pump nozzles. A few years ago, the injection pressure in the “Common Rail” systems did not exceed 130 MPa, but soon the designers reached the threshold of 160 MPa. However, this is not the peak: Toyota has already announced 180 MPa (today the pump nozzles of serial motors have reached 205 MPa). One of the first samples is the latest D-4D Clean Power engine.
In pump nozzles, the injection law is set once and for all by the cross-section of the channels and the stiffness of the springs, you can only control the start of the injection and the amount of fuel supplied. And in most currently used circuits with a common line, the solenoids command the opening of nozzles. In Toyota, the piezo-elements quickly control the injection process.
Each D-4D Clean Power nozzle is equipped with a block of ceramic piezoelectric elements. When voltage is applied, the elements expand almost instantly, allowing you to quickly open the nozzle. The speed of the piezoelectric elements and the high pressure in the “common line” helps to inject the entire volume of fuel in a shorter period of time. Experts say that the injection performance is improved, contributing to a finer atomization of fuel and efficient combustion. The D-4D Clean Power motor is also distinguished by a reduced compression ratio and high boost pressure - for the benefit of efficiency. And specially designed ceramic glow plugs facilitate cold starting.
These are, so to speak, active measures to achieve profitability and high environmental performance. But there are also “passive” ones. During the development of the D-CAT device, Toyota received more than 1, 600 patents. The heart of the system is a four-stage catalytic converter. And afterburning and nitrogen oxides, and soot particles! The effectiveness of the converter directly depends on the control electronics of the "Common Rail". But even high injection technologies are not able to provide the ideal exhaust composition. It was necessary to equip the exhaust manifold with another fifth nozzle - Exhaust Port Injector (EPI). Periodically, EPI injects an additional portion of the fuel and restores the gas composition necessary for the effective operation of the D-CAT converter.
We illustrate this complex construction with numbers. Firstly, depending on the operating mode, the exhaust toxicity of new engines is 50–80% less than the strict European Euro IV standards require. Secondly, the serial engine promises to outdo the power of all competitors in the "weight category" from 1.9 to 2.2 liters. According to Toyota specialists, the engine power will reach 132 kW / 180 l. s., and torque - 400 N.m.
WHERE DOES THE WIND BLOW?
Diesels are increasingly appearing under the hoods of prestigious cars, often becoming one of the most powerful in the engine range. One of the leaders in the diesel race for kilowatts is BMW. A striking example is the technology of Variable Twin Turbo ("Biturbo") in relation to diesel engines.
They decided to combine the old idea of a perfectly balanced in-line Six with the advanced technology of a supercharged in a 3-liter engine for the BMW 535d sedan and station wagon. We described his work in detail (ЗР, 2004, No. 9). And here we recall the achieved results: 500 N.m of torque already at 1250 rpm, 560 N.m at 1750 rpm. Maximum power 200 kW / 272 liters. with. at 4400 rpm This engine with a specific power of 90 liters. s./l and a torque of 187 N.m / l holds an unofficial record among serial diesels.
One of the most difficult tasks, according to the firm, was to synchronize the operation of the turbines and control of the bypass air valve. The problem was solved using a processor. Electronics also allowed the motor to fit into the framework of Euro IV. Of course, not without the help of a particulate filter: all the latest BMW diesel engines are equipped with it “by default”.
The dynamic performance of the BMW 535d is impressive: up to 100 km / h, the car accelerates in just 6.6 s, and the maximum speed is likely to be higher than 250 km / h “allowed” by electronics.
Milestone 100 l. s / l for serial supercharged diesel engines has not yet been overcome. How long can he stand? To achieve such characteristics, the engine must develop a boost pressure of at least 200 kPa. It will be difficult for designers to provide an engine with such a high boost pressure with an acceptable, convenient external speed characteristic. A disadvantage of the known boosting devices - with increasing pressure, the range of revolutions narrows in which a high moment is available.
A sophisticated boost system on a BMW is just one solution. Perhaps the designers would prefer an exotic turbocharger, spun by an auxiliary electric motor, or equip the car with some fancy variator with an unprecedentedly wide range of gear ratios? Or an automated eight-speed gearbox? And you can also include such a diesel engine in the hybrid power plant, which will correct the “wrong” curve. Engineers have something to think about, and students where to show imagination.
In recent years, the question has become relevant - how many cylinders does a modern diesel engine need in a particular class? Now they produce not only multi-cylinder cars, but also three-cylinder “kids”. The number of the latter will increase in the near future: naturally aspirated diesel engines are finally becoming a thing of the past, and the power of two-liter supercharged units is excessive for miniature cars. Why two-liter? With four cylinders they have a volume close to optimum of each - 500 cm3. The larger the cylinder volume, the more efficient the combustion process will be, but high speeds are not for engines with heavy pistons and connecting rods, and the dimensions of the power unit are greatly increased. With a small (about 300 cm3) thermodynamic efficiency noticeably suffers, and with it economics.
Mercedes-Benz Smart Fo-Fo engines are particularly interesting in the non-standard three-cylinder design. They develop 50 kW / 68 l. with. and 70 kW / 96 l. with., and the volume is quite "adult" - 1.5 liters. The units are extremely compact and develop a high torque (160 and 210 N.m) at 1600 and 1800 rpm with an average fuel consumption of only 4.6 liters. The injection pressure in the "Common Rail" reaches 160 MPa - hence the exceptional fineness of the spray and favorable combustion conditions.
But what about the unbalanced forces of inertia? This problem is solved by balancing shafts and a two-mass flywheel. By the way, now they are not uncommon on four-cylinder engines.
The “modernity” of a passenger diesel is determined not by the block and cylinder head, but primarily by the fuel equipment and boost control. Without them, record levels cannot be achieved. However, do not discount the fuel problem. With rising oil prices, synthetic fuels will be in demand, the raw materials for which can be vegetable oils, coal, and natural gas. Oil companies are investing heavily in alternative fuel technology. They are designed to help not only solve environmental problems, but also achieve even higher power and economic indicators.