Assuming that the fuel is clean and water-free, the most important quality is its cetane value, which can be determined with fuel hydrometer. A good No. 2 diesel has a specific gravity of 0.840 or higher at 60 degree Farenheit. No. 1 diesel can reduce power outputs by as much as 7% over No. 2 fuel. Blending the two fuels, a common practice in cold climates, results in correspondingly less power.

A clean fuel will produce some effective output, especially for specific brand that produce comfort car such as audi, it is necessary filling quality fuel for maximizing its mechanical system. Some audi leasing and authorized garage would give you detail instruction for the best performance of your car.

Most failures involve the fuel system. This system consists of three circuits, each operating at a different pressure.

• Low-pressure circuit. This includes the tank strainer, in-tank pump (on many vehicles), water-fuel separator, filter(s), and lift pump. Pressures vary with the application, but rarely exceed 75 psi.

• Fuel-return circuit. Operating at almost zero pressure, the return line conveys surplus fuel from the injectors back to the tank, filter, or to the inlet side of injector pump. Many of these systems include a restrictor orifice between the fuel-supply line and the return line. The orifice can clog, closing off the fuel return. Air leaks become a matter of concern when fuel is returned to the filter or injector pump, and not to the tank.

• High-pressure circuit. The high-pressure circuit connects the discharge side of the injector pump with the injectors. For many applications, the connecting plumbing takes the form of dedicated lines from pump to the individual injectors. A more modern approach is to supply the injectors from a common manifold, or rail. The third alternative does away with the external high-pressure circuit by employing unit injectors (UIs). Each UI is a self-contained unit, with its own high-pressure pump operated by an engine-driven camshaft or, in the case of the Hydraulic Electronic Unit Injector (HEUI), by oil pressure. The unit pump system (UPS) is a hybrid, with each injector served by a dedicated pump plunger operating off the engine camshaft. Plunger-to-injector lines are pressurized.

Some engine malfunction usually indicated by uncommon engine behavior such as unable to start the engine, smoke cause of fuel contribution, speed loss, and many others that will be explained as below:

Engine cranks slowly, does not start

Starting system malfunction
Recharge batteries if cranking voltage drops below 9.5V or electrolyte reads less than 1.140 when tested with a hydrometer. Clean battery terminals. Perform starting system check.

High parasitic loads
Check for binds in driven equipment, overly tight drive belts, shaft misalignments.

Crankshaft viscosity bound
Dark, sticky residue on the dipstick can indicate presence of antifreeze (ethylene glycol) in oil. Have oil analyzed.

Engine fails to develop normal power
EMS-related fault
Retrieve trouble codes.

Insufficient fuel supply
Replace filters, check transfer pump output, cap vent, and air in the system.

Contaminated fuel
Verify fuel quality.

Injection timing error
Check injector-pump timing.

High-pressure fuel system
Inspect high-pressure fuel system for leaks and air malfunction entrapment. Verify pump output pressure. If necessary
have pump recalibrated.

Air inlet restriction
Change air-filter element.

Exhaust restriction
Inspect exhaust piping, test for excessive back pressure.

Insufficient turbo boost
Change air-filter element, check boost pressure and for exhaust leaks upstream of the turbo.

Loss of engine compression
Check engine cylinder compression.

Operators often judge a truck’s power, or lack of it, by how fast the truck runs. In other words, operators look at maximum rated horsepower available at full governed rpm. But expected road speeds may be unrealistic. For example, numerically low axle ratios can, up to a point, increase top speed, but at the cost of reduced acceleration and less startability, a term that is defined below.

Other factors that influence top speed are loaded weight, road conditions, wind resistance (which can double when loads are carried outside of the vehicle bodywork), and altitude. Naturally aspirated engines lose about 3% of their rated power per 1000 ft of altitude above sea level.

Other factors to consider are the ability of the vehicle to cope with grades. Startability is expressed as the percentage grade the vehicle can climb from a dead stop. A fully loaded general-purpose truck should be able to get moving up a 10% grade in low gear. Off-road vehicles should be able to negotiate 20% grades, with little or no clutch slippage. Startability is a function of the lowest gear ratio and the torque available at 800–1000 rpm.

Gradeability is the percentage grade a truck can climb from a running start while holding a steady speed. No vehicle claiming to be self-propelled should have a gradeability of less than 6%. Gradeability depends upon maximum torque the engine is capable of multiplied by intermediate gearing.

Caterpillar and other engine manufacturers can provide assistance for sizing the engine to the particular application. But it’s useful to have some understanding of how power requirements are calculated.

Vehicle engines traditionally use a three-point mounting system, with a single point forward around which the unit can pivot, and with two points at the flywheel housing or transmission. For some engines the forward mount takes the form of an extension, or trunnion, at the crankshaft centerline. A sleeve locates the trunnion laterally, while permitting the engine to rotate. In order to simplify mounting and give more control over resiliency, other engines employ a rigid bracket bolted to the timing cover and extending out either side to rubber mounts on the frame.

On many applications the transmission cantilevers off the engine block without much additional support. The bending moment imposed by the overhung load on the flywheel housing should be calculated and compared against factory specs for the engine.

EPA regulations apply only to sulfur content and to cetane number/aromatic content. Other fuel qualities, such as lubricity, filterability, and viscosity, are left to the discretion of the refiner. As a general rule, large truck stops provide the best, most consistent fuel.

• Cetane number (CN) and aromatic content refer to the ignition quality of the fuel. U.S. regulations permit 40 CN fuel if the aromatic content does not exceed 35%. In Europe diesel fuel must have a CN of at least 51. Aromatic content expresses the ignition quality of the fuel. High-octane fuels, such as aviation gasoline, have low CNs and barely support diesel combustion. Conversely, ether and amyl nitrate, which detonate violently in SI engines, are widely used as diesel starting fluids.
• API (American Petroleum Institute) gravity is an index of fuel density and, by extension, its caloric value. Heavier fuels produce more energy per injected volume.
• Viscosity also affects performance. Less viscous fuels atomize better and produce less exhaust smoke. But extremely light fuel upsets calibration by leaking past pump plungers. Thick, highly viscous fuels increase delivery pressures and pumping loads.
• Flash point, or the temperature at which the fuel releases ignitable vapors, is a safety consideration.

Buttressed main-bearing caps, pressed into the block and often cross-drilled, support the crankshaft. Pistons run against replaceable liners, whose metallurgy can be precisely controlled.

Until exhaust gas recirculation became the norm, heavy truck piston rings could, on occasion, go for a million miles between replacements. An early Caterpillar 3176 truck engine was returned to the factory for tear down after logging more than 600,000 miles. Main and connecting-rod bearings had been replaced (at 450,000 and 225,000 miles, respectively) and were not available for examination. The parts were said to be in good condition.

The crankshaft remained within tolerance, as did the rocker arms, camshaft journals, and lower block casting. Valves showed normal wear, but were judged reusable. Connecting rods could have gone another 400,000 miles and pistons for 200,000 miles. The original honing marks were still visible on the cylinder liners.

But Caterpillar was not satisfied, and has since made a series of major revisions to the 3176, including redesigned pistons, rings, connecting rods, head gasket, rocker shafts, injectors, and water pump. Crankshaft rigidity has been improved, and tooling developed to give the cylinder liners an even more durable finish.

Industrial engines are less than perfect, and when mated with digital technology the problems multiply. Many of the worst offenders are clones, that is, diesels derived from existing SI engines. No one who was around at the time can forget the 1978 Oldsmobile Delta 88 Royale that sheared head bolts, crankshafts, and almost everything in between.

The improvement of passenger car fuel economy represents a very important goal that will determine the future use of SI engines instead of the small, high-speed, diesel engines.

The thermal efficiency of the GDI engine can be enhanced by increasing the compression ratio, or by using a lean mixture, thereby reducing the throttling losses and wall heat losses. As outlined conceptually by Karl et al.

As is well known, the effect of this higher compression ratio on fuel economy is significant.
In summary, the major factors contributing to the improved BSFC of a GDI engine over that of a conventional PFI engine are:
• decreased pumping losses due to unthrottled part-load operation using overall lean mixtures;
• increased knock-limited compression ratio due to lower end-gas temperatures;
• increased cooling of the intake charge due to in-cylinder injection during induction;
• increased cycle efficiency to the incrementally higher specific heat ratio of lean mixtures;
• decreased cylinder wall and combustion chamber heat loss due to stratified combustion.

Many factors affect the net fuel economy improvement that may result from applying GDI technology to an engine-vehicle system. Without knowing the details of the baseline engine and/or vehicle, caution must be used in attributing the fraction of any reported fuel economy improvement that result from individual segments of the direct injection technology.

• Spray characteristics:
o appropriate cone angle to insure good air utilization for early injection;
o appropriate fuel mass distribution within the cone to avoid fuel wetting of the cylinder wall and the piston crown outside of the bowl;
o appropriate penetration characteristics to insure good air utilization for early injection while avoiding wall impingement;
o small sac volume and no after-injection.

• Optimized spray-axis angle to achieve a combustible mixture at the spark plug gap while avoiding wall impingement.
• Injection timing for the early injection, homogeneous operating mode should be advanced to take full advantage of in-cylinder charge cooling.
• Spray should “chase” the piston to minimize spray/piston-crown impingement during early injection.
• Injection timing for the stratified-charge operating mode:
o timing as retarded as possible to minimize excessive fuel diffusion;
o timing advanced enough to enable reliable ignition;
o sufficient injection rate and low-pulse-width stability
to reliably inject small fuel quantities.
• Optimized combustion chamber geometry.
• Optimized combination of the above parameters.

In contrast, the primary fuel spray characteristics of a port fuel injector generally have much less influence on the subsequent combustion event, mainly due to the integrating fuel effects of the residence time on the closed valve, and due to the secondary atomization that occurs as the induction air flows through the valve opening.

For direct injection in both GDI and diesel engines, however, the mixture preparation time is significantly less than is available for port fuel injection, and there is much more dependence on the primary spray characteristics to prepare and distribute the fuel to the optimum locations. It is well established that a port-injected gasoline engine can operate quite acceptably using a spray of 200 Ixm SMD, whereas a GDI engine will generally require atomization that is an order of magnitude finer.

Even though a relatively complete correlation database has been established for diesel sprays [67,68], the bulk of these correlations unfortunately cannot be applied to predict the characteristics of DI gasoline sprays. This is the result of significant differences in fuel properties, injection pressure levels, droplet velocities and size ranges, ambient pressure and temperature levels, and droplet drag regimes.

It may thus be seen that the correlation and predictive characterization of the fuel sprays from GDI injectors represent a new and important research area. Until such time as a comprehensive and proven correlation database is available, the spray parameters for individual injector designs will have to be measured in order to provide data for CFD model initiation and design comparisons.

The two terms are related:
Horsepower = torque x 2pi x rpm. Revolutions per minute is the time component.
Torque = displacement x 4pi x bmep.
The latter term, brake mean effective pressure, is the average pressure applied to the piston during the expansion stroke.

High-performance diesels, such as used in European automobiles, develop maximum horsepower at around 5000 rpm. Equivalent SI auto engines can turn almost twice as fast. Since rpm is part of the hp formula, these diesels fall short in the power department. An SI-powered car will have a higher top speed.

But, thanks to high effective brake mean pressures, diesels have the advantage of superior torque. A diesel-powered BMW or Mercedes-Benz easily out-accelerates its gasoline-powered cousins.

In a CI engine, air undergoes compression before fuel is admitted. Injectors open late during the compression stroke as the piston approaches tdc. Compressing air, rather than a mix of air and fuel, improves the thermal efficiency of diesel engines. To understand why would require a course in thermodynamics; suffice to say that air contains more latent heat than does a mixture of air and vaporized fuel.

CI engines dispense with the throttle plate—the same amount of air enters the cylinders at all engine speeds. Typically, idle-speed air consumption averages about 100 lb of air per pound of fuel; at high speed or under heavy load, the additional fuel supplied drops the ratio to about 20:1.

Since diesel air flow remains constant, the power output depends upon the amount of fuel delivered. As power requirements increase, the injectors deliver more fuel than can be burned with available oxygen. The exhaust turns black with partially oxidized fuel. How much smoke can be tolerated depends upon the regulatory climate, but the smoke limit always puts a ceiling on power output.

To get around this restriction, many diesels incorporate an air pump in the form of an exhaust-driven turbocharger or a mechanical supercharger. Forced induction can double power outputs without violating the smoke limit. And, as far as turbochargers are concerned, the supercharge effect is free. That is, the energy that drives the turbo would otherwise be wasted out the exhaust pipe as heat and exhaust-gas velocity.

The absence of an air restriction and an ignition system that operates as a function of engine architecture can wrest control of the engine from the operator. All that’s needed is for significant amounts of crankcase oil to find its way into the combustion chambers. Oil might be drawn into the chambers past worn piston rings or from a failed turbocharger seal. Some industrial engines have an air trip on the intake manifold for this contingency, but many do not. A runaway engine generally accelerates itself to perdition because few operators have the presence of mind to engage the air trip or stuff a rag into the intake.