Engineering workshop

Diesel Engine Combustion Efficiency

noreply@blogger.com (Unknown) — Sun, 30 May 2010 04:58:00 +0000

Index Key: ENG048
Author: gerald j ballmann
Subject: Diesel engine combustion efficiency.
1) What limits the compression ratio of a diesel engine?
2) What is the best fuel to use in a diesel engine for maximum efficiency?

Response #: 1 of 2
Author: daniel n koury jr
The compression ratio for a particular engine is limited by how strong the
engine block is. Too much pressure (compression) and something will break.
The best fuel will also depend on the design of the engine. But as a
general rule, the greater the energy content of the fuel, the greater the
efficiency (at least in terms of miles per gallon or km per liter). Water
has a low energy content and would not make a good fuel for example.

Response #: 2 of 2
Author: david r munoz
The limits to compression ratio are based on the knock limits of the fuel.
Knock is the term used to describe the auto ignition that occurs when a fuel
ignites because the pressure in the cylinder is such that combustion occurs.
In a spark ignited engine, it is best if the spark control the ignition,
since timing of the piston motion with the motion of the flame front is
critical to the operation of an efficient engine.
In a diesel engine, one relies on auto ignition of the fuel because the
engine is basically compression ignited (there is no spark plug). There-

fore, we want the fuel to be autoignited. However, some types of combustion
waves move faster than others. There are waves called detonation waves that
contribute to sonic velocities of the hot gases in the cylinder. It is
generally, the nonuniformity of the pressure within the cylinder that are
responsible for knock. Some believe that these nonuniformities are due to
detonation and others believe they are due simply to nonuniform combustion
or auto ignition in the cylinder.
The knock limits for a fuel are determined on a special single cylinder
engine called a CFR engine. On this engine, the compression ration can be
gradually changed. In general, a fuel is burned in the engine and the
compression ratio is changed high and low until the engine begins to shake.
This is known as the knock limit for the fuel. The higher the knock limit,
the higher the compression ratio.

Measure Indicated Power in Diesel Engine with Indicator Diagram

noreply@blogger.com (Unknown) — Sun, 30 May 2010 04:52:00 +0000

The burning of fuel in an engine cylinder (2 stroke or 4 stroke diesel engine) will result in the production of power at an output shaft, some of the power produced in the cylinder will be used to drive the rotating masses of the engine.

Typical indicator diagram for a 2 stroke engine is shown in figure below. The area within the diagram represents the work done within the cylinder in one cycle.
The area can be measured by an instrument known as 'Planimeter' or by the use of the mid ordinates rule. [On modern engines this diagram can be continuously taken by employing two transducers, one pressure transducer in the combustion space and other transducer on the shaft. Through the computer we can thus get on line indicated diagram and power of all cylinders.]

The area is then divided by the length of the diagram in order to obtain mean height. This mean height, when multiplied by the spring scale of the indicator mechanism, gives the indicated mean effective pressures for the cylinder. The mean effective or average pressure [Pm] can now be used to determine the workdone in the cylinder.

Calculations

Area of the indicator diagram = a [mm²]

Average height of the diagram = a [mm²] / l [mm]

Average mean indicator pressure = a [mm²] / l [mm] x k [bar / mm]

or P_m= ( a / l ) x k [bar]

where k = spring scale in bar per mm

Work done in one cycle = Mean Indicated Pressure x Area of the Piston x Length of stroke

= [P_m] x [A] x [L]

To obtain the power of this unit, it is necessary to determine the rate at which work is done,

i.e. multiply work by number of power strokes in one second.

Now, Indicated Power of Unit [i_p] =

Mean Indicated Pressure [P_m] x Area of Piston [A] x Length of Stroke [L] x Number of Power Strokes per Second [N]

Indicated Power of Unit = Pm L A N

Fuel Injector Testing

noreply@blogger.com (Unknown) — Sun, 30 May 2010 04:52:00 +0000

Mount he fuel injector in its test rig and connect up the oil supply. Under no circumstances should hands be placed under the injector spray. The high velocity oil jet can penetrate the skin and cause blood poisoning. With the injector priming valve open, operate the hand pump to prime the injector. Once the fuel flows from the priming valve it can be closed.

Oil Container

Pressure Gauge

Shut off valve

Pump lever

Test pump

Injector

High Pressure fuel pump

Operate the pump rapidly for several strokes. The injector should open with a high pitched chatter and fuel should be emitted in a fine cloud. After the injector opens, check to make sure the pressure does not fall off too quickly.

To test for the tightness between the nozzle needle and seat, operate the hand pump slowly to gradually increase the pressure until it is just below opening pressure. Maintain the pressure for a few seconds and ensure injector is not dripping.

To test for tightness between needle and guide, operate the hand pump to increase pressure until it is just below opening pressure. See how long it takes the pressure to fall off. If the pressure falls quickly the needle and guide should be replaced.

Where nozzles are cooled internally, these spaces should be pressure tested to check for tightness. Blank off one of the fuel valve cooling connections and fill the injector cooling space with water or fuel, depending upon the cooling medium. Then connect a low pressure air supply to the other connection. Leave the air on for a short period of time and test for internal or external leakage.

How Diesel Engines work

noreply@blogger.com (Unknown) — Sun, 30 May 2010 04:52:00 +0000

Diesel Engine is a type of internal combustion engine (one from which work is obtained by compression of the fuel within the cylinders themselves) which operates on the constant pressure or diesel cycle principle. Fuel is admitted directly into the cylinder and combustion takes place as a result of the heat of compression.
In these engines, gas pressure in the cylinder acts on the piston, forcing it down during the power stroke to drive the crankshaft through connecting rods. The extreme positions reached by the piston correspond to the top and bottom dead center positions (TDC & BDC) of the crank and are so designated. The inside diameter of the cylinder is the bore. The distance traveled between dead centers (TDC &BDC) is the stroke, corresponding volume is the swept volume, or displacement, of the cylinder. The cylinder volume above piston when piston is at TDC is called clearance volume. Similarly the cylinder volume above piston when piston is at BDC is called cylinder volume. The ratio of the cylinder volume to the clearance volume is the nominal compression ratio.
The greater combustion pressure is the result of the higher compression ratio used by diesel engines. Compression ratio is a measure of how much the engine compresses the air inside the cylinder. In a diesel engine compression ratio ranges from 14:1to as high as 24:1 are commonly used. Higher compression ratios are possible because only air is compressed, and then the fuel is injected. This is one of the factors that allows the diesel engine to be so efficient.

external electrical connectors broke/corroded

noreply@blogger.com (Unknown) — Sun, 21 Mar 2010 09:01:00 +0000

CAUSE OF FAILURE 6...mishandling during installation/removal/testing, water/moisture leaking past injector plug connector, inadequate vehicle maintenance, improper storage.

EFFECTS OF FAILURE 6...no firing, intermittant firing, or weak firing of injector due to poor electrical conductivity , poor engine performance, poor fuel economy. engine overheating, potential engine damage, overfueling of other cylinders as 02 sensor reads excess 02 in exhaust and adjusts "rich" to compensate.

injector pintle doesn't fully seat on orifice

noreply@blogger.com (Unknown) — Sun, 21 Mar 2010 09:01:00 +0000

CAUSE OF FAILURE 5...fuel additives "baked" on pintle or orifice, weak injector return spring, rust/corrosion internal to injector body.

EFFECT OF FAILURE 5...leaking fuel injector, after shutdown fuel leak in affected cylinder (causing hard start), overfueling of affected cylinder with resultant underfueling of remaining cylinders in the "closed loop" system, potential for damage to O2 sensor or "cats".

Body or mechanical joint leak in injector body

noreply@blogger.com (Unknown) — Sun, 21 Mar 2010 09:00:00 +0000

CAUSE OF FAILURE 4...Defective manufacturing and testing, overheating of injector from cooling system failure, ignition system failure, incorrect timing, improper "handling" during installation/removal/storage/shipping, etc.

EFFECT OF FAILURE 4...High potential for engine fuel fire (dependent on location of leak), poor engine performance, poor fuel economy, potential for engine damage.

Injector windings don't lift pintle, seized pintle, or slow pintle cycling

noreply@blogger.com (Unknown) — Sun, 21 Mar 2010 08:59:00 +0000

CAUSE OF FAILURE 3...injector coil windings overheated from cooling system failure or ignition failure, with windings losing their magnetic performance; open (broken) windings; shorted (grounded) windings; seized pintle from internal injector corrosion (engine has set too long without running causing the injector to rust internally, petrol contamination with water, or cycling of injector without fuel flow to act as cooling agent and lubricant).

EFFECTS OF FAILURE 3...(A) If injector pintle is "off" the seat...overfueling of affected cylinder with resultant underfueling of remaining cylinders within "closed loop", poor engine performance, poor fuel economy, possible O2 sensor damage, potential engine overheating and engine damage, hard or no start, fuel leaks after shutdown. (B)If injector pintle is "on" the seat...underfueling/no fueling of affected cylinder with resultant overfueling of remaining cylinders with "closed loop" system, poor engine performance, poor fuel economy, O2 sensor damage, engine/piston/ring damage.

Injector filters become clogged

noreply@blogger.com (Unknown) — Sun, 21 Mar 2010 08:58:00 +0000

CAUSE OF FAILURE 2..."Foreign particles" in fuel tank(s) or fuel lines, or fuel rail. Foreign particles in almost all instances, will be rust. Larger rust particles may be collected within the injector filter, or the fuel filter, and reduce fuel flow. Microscopic rust particles may also pass thru the injector filter, and cause the spray pattern to alter, fuel flow to alter, and/or the injector pintle to not seat properly. This is a common problem on vehicles that have sat unattended, or suffered from lack of routine maintenance. Incorrect fuel tank fuel filter; holes/tears in fuel tank fuel filter; breakdown/degradation of interior wall of fuel supply line; breakdown/degradation of interior wall of fuel injector hose, and rust in the fuel rail.

EFFECTS OF FAILURE 2...the injectors leak at the pintle and/or the spray pattern is altered, and/or the fuel flow is altered. Lack of engine power from underfueling; potential for engine overheating; remaining injectors/cylinders are overfueled to compensate for underfueled injectors/cylinders as the "closed loop" O2 system attempts to maintain stoiciometric ratio.

Fuel Injectors Work

noreply@blogger.com (Unknown) — Sun, 21 Mar 2010 08:56:00 +0000

The TBI system took the place of the carburetor as governmental automobile pollution standards increased , as well as a simultaneous increase in consumer requirements for greater fuel economy. In the TBI system, a throttle body sits atop the engine in the location where the carburetor use to reside. The throttle body in fact looks very much like a carburetor, however it performs very much differently. Located within the throttle body are one or two injectors (depending on the vehicle). When the engine is started, a continuous spray of pressurized fuel is discharged thru the injectors, into the intake manifold, and from there on to the cylinders for combustion. The injectors in the TBI system are always open, and spraying fuel when the engine is on. They do not pulse on and off. Furthermore, the one or two injectors are supplying fuel to every cylinder collectively, as did the carburetor, but with much greater precision. While the TBI system, and the advances in engine management that went along with it, were a great improvement over the carburetor, there were yet more advances to be made. In the TBI system, each cylinder pulled in on the intake stroke, the volume of air/fuel available at the back of the intake valve. If the cylinders were closer to the throttle body, they were going to get more air/fuel than than those cylinders farther away. The TBI had greater efficiency over the carburetor, but still needing a more balanced air/fuel delivery, which in turn would further reduce exhaust emission, increase fuel economy, and increase engine performance.

So, petrol prices continued to climb and regulations on air pollution continued to get tougher. And along comes the MPI injection system. This system replaced the TBI and is now the only system in production by auto manufacturers. In an MPI system, there is no throttle body. Each cylinder now has its very own fuel injector, located within the intake manifold and delivering fuel directly behind the intake valve. A major improvement, in that now each cylinder has its own individual fuel supply, and the balancing of air/fuel volume between all cylinders is much more precise.

The fuel injector is an electrically operated solenoid valve. It consists of a metal (or composite molded) body, coil windings, an electrical connector, a pintle, pintle spring, fuel filter, orifice, pintle cap, o-rings, and spacers. Current is delivered thru the injector coil, when the ignition key is turned on. On cranking, the injector driver circuit grounds the injector, the coil winding is energized and creates a magnetic field (a magnet). The magnetic field then pulls the injector pintle from its seat (the orifice) allowing pressurized fuel to flow through the injector, through the orifice, to the intake valve, and into the cylinder. When the injector ground is cut off, the magentic field collapses and the pintle is pushed back by a spring to its home, and fuel delivery stops. The actual driver circuitry is much more complex than stated. However, that is another topic.

The solenoid valve, in fact is a rather simple device, yet extraordinary at the same time. The history and principle of the solenoid, is attributed to the French physist, Andre-Marie Ampere, in the early 1800's. Note the name Ampere... (amps)... sound familiar? Tis doubtful that Ampere could have envisioned his discovery of magnetism induced from electrically energizing a coil winding, would literally, several hundred years later, been applied to so many hundreds of million components, that it literally "moves the world".

As brilliant, or a simple, as the injector is, depending on your perspective, it has but one and only one purpose. That is to allow fuel to flow into the cylinder. BUT, it must do so within the following parameters. It must filter the fuel, it must deliver the proper volume of fuel, it must deliver the proper fuel spray pattern, and it must close and seal properly. The injector has no "mind of its own". It has no self-correcting capabilities. Either it works within its manufactured specifications, or it doesn't.

Consider this. On the V12 HE engine, each injector fires once every other crankshaft revolution, two revolutions being one complete engine cycle. At 3,000rpm, when this particular engine is just beginning to reach its powerband, and also where we would most frequently be on the tach, each injector is firing at a rate of 25 times/second. At 6,000rpm...50 times/second. In one hour of operation at 3,000rpm, each injector has cycled 90,000 times. If you drive 12,000miles/year...a pretty astonishing 18,000,000 times/per injector!! And remember, this is a mechanical device with moving parts, coils windings energizing and collapsing, pintle valves up and down, and in an extremely hot environment. And it's doing this in the milliseconds....thousands of a second!! And if you want to think about its fuel flow...figure 18mpg at 12,000miles/year and you get 667 gallons/year or 55 gallons of petrol per injector. That's a 55 gallon oil drum full. For those of you with older vehicles...well...you can do the math. But... I will add one more. A vehicle with 100,000 miles on the clock...150 million cycles/per injector. That's a pretty hefty demand on such a small part, which is why they are so damned expensive to buy!

With such severe duty cycle, the injector has to be subject to failure....mechanically, electrically, or fouling from the volumes of fuel it flows. There are several failure modes that can occur...which I explain on another page. The only way to definitively know if injectors are operating within specifications, is to pull the injectors and have them "bench tested" off the vehicle, where they can be tested electrically, visually inspected for proper fuel spray pattern, flow tested for proper volume delivery, and leak tested for pintle/seat or mechanical leaks . They can then be cleaned, serviced, and in most cases restored to service, eliminating the high cost for new injectors. Remember...you can't fix what you can't see!

Engine speed governor

noreply@blogger.com (Unknown) — Sat, 27 Feb 2010 04:57:00 +0000

I have built a small diesel generator but the mechanical governor does not seem to respond quick enough.I would like to build an electronic governor that will also have overspeed shutdown protection.

I have built a couple of simple electronic controllers for my biogas projects from schematics but I am certainly not an electronics tech.

The engine is from a refridgeration unit that was electroniclly controlled so their is a sensor over the flywheel for speed siginal to the controller.

If anyone out their can help with this project it would be very much appreciated.

Crankshaft Bearing Failure

noreply@blogger.com (Unknown) — Sat, 27 Feb 2010 04:53:00 +0000

My 11 year-old 1000-hour 38 HP Yanmar 3JH2E Diesel on my 36 foot sailboat experienced crankshaft bearing failure. The center bearing disintegrated while the other two bearings remained in perfect condition.

The circumstances were the prop shaft became entangled in lobster fishing gear during a passage through the Cape Cod Canal. In order to make any headway to keep control and get to a safe anchorage, I had to apply full emergency power to a heavily overloaded engine. The center crankshaft bearing failed, while the other two survived. Because the crankshaft was heavily scored, the engine was a total loss, and needed replacement.

The insurance surveyor, claimed that this was a "mechanical failure due to latent defect" "or possibly faulty maintenance" and recommended that the claim be denied, despite clear evidence that the prop and shaft were entangled. I would like your opinion of the possibility that heavy lugging at high power settings caused heating, and overloading, and could be responsible for the center bearing being spun on the crankshaft.

Response:

These things are hard to know with certainty. Some observations:

A properly set up and maintained diesel that is properly propped should be able to run at wide open throttle for hours without problem. Even the highest HP configurations are rated for 30 minutes at full RPM. Which is to say, full emergency power should not be a problem.
An over-heated or overloaded diesel will have a short life with piston damage and cylinder scoring being the most common catastrophic failures. Overheat will damage valve seals and weaken piston rings as well, even if there is no failure evident.
Something wrapped around the prop shaft will over-load if run wide open and it may yield catastrophic failure.

In your case, you were essentially running wide open with what is effectively an over-propped engine. The engine probably is properly propped but, with the shaft bound up, it's as though you were over-propped. This will shorten life and could lead to bearing failure. Bearing failure is not the most common failure mode but it can happen that during over-heat, the bearing set with the least clearance can bind-up and spin.

Personally, I would either drift if away from danger or drop anchored to slow the drift if near shore and free up the shaft when faced with this problem in the future.

The failure you have encountered could have been contributed to by dirty oil or debris in the oil as well. If the other bearings are not scored and look in good shape, you have good evidence that this isn't the case.

If the engine has few hours and is very well maintained, you have a good case. Is the engine room super clean, the engines expertly maintained, etc. If so, you should push for a better answer from your insurance company. If not, you should accept it as a combination of wear, age, maintenance, and bad luck. It's a gray enough area that the judgment call will be influenced by many factors including age, hours, maintenance, cleanliness, the location and conditions you faced (was it absolutely required that you press on?), the mood of the investigator, the phase of the moon, ...

Maxi Fly Wheel

noreply@blogger.com (Unknown) — Sat, 27 Feb 2010 04:50:00 +0000

Description: Peugeot Sport 106 maxi flywheel. This is a homoligated flywheel for 106. Banned for Super 1600 but is fine to use under Group A6. This flywheel is very light and not suitable for gearboxes with long final drives. As you will struggle on touring stages (hill starts). However the pickup of the engine in the stage is chalk and cheese compared to the standard flywheel.

Trans Brace

noreply@blogger.com (Unknown) — Fri, 19 Feb 2010 11:39:00 +0000

I believe in maximizing the rigidity of the block / transmission assembly. We had to reconfigure Honda's brace to fit properly with the Moroso oil pan. Details like this are important to building a long-lasting combination.

Twin Disk cm

noreply@blogger.com (Unknown) — Fri, 19 Feb 2010 11:37:00 +0000

Lots of pieces fit into small spaces with this package. Note the sculpting to reduce flywheel mass and the small diameter of the pressure plate, disks and floaters. This set-up is extremely lightweight and capable of handling a lot of abuse, including shifts over 10K.

Header Flange

noreply@blogger.com (Unknown) — Fri, 19 Feb 2010 11:35:00 +0000

Note that the header primary pipes are configured to work with our raised port roofs.
Oil heater? We'll make sure there's some separation here before installation. I'm also raising secondary pipes and collector about 1.5" for better in-vehicle ground clearance, which is important on the streets of Ft. Worth.

HDon't be mislead by the picture, but it's imperative that the header (and intake) gaskets do not hang in the way of the flow. If you don'eader Gasket

noreply@blogger.com (Unknown) — Fri, 19 Feb 2010 11:34:00 +0000

Don't be mislead by the picture, but it's imperative that the header (and intake) gaskets do not hang in the way of the flow. If you don't trim the gaskets, you're potentially sacrificing any possible gains from porting. We trim the gaskets to be approximately .050" larger all the way around the port. This gasket is situated ahead of the flange on the studs, producing the illusion that the openings are much larger than the ports.

Hytech Header

noreply@blogger.com (Unknown) — Fri, 19 Feb 2010 11:33:00 +0000

Checking for fitment on our "killer" header from John at Hytech. Note that he configured it for AC clearance. This header is the veteran of many dyno pulls on similar 2-liter engines we've built, so it's a known quantity.

Block Fittings

noreply@blogger.com (Unknown) — Fri, 19 Feb 2010 11:31:00 +0000

We're using two breather tanks on this high-revving engine. The block fittings are the same ones we sell, with the anti-siphon tubes for increased efficiency in separating oil. Note the sealant that's standard issue on the threads.

Balancer TDC Mark

noreply@blogger.com (Unknown) — Fri, 19 Feb 2010 11:30:00 +0000

Prior to installation, I always mark the harmonic balancer 180 degrees opposite the TDC mark to facilitate setting the valves. Note that this is a stock (neutral-balanced) ITR balancer we're using. Always use a new crank bolt for the installation.

Torquing Cam Bolts

noreply@blogger.com (Unknown) — Fri, 19 Feb 2010 11:29:00 +0000

Torque the cam bolts to factory specs. Do not use an impact to tighten the bolts... Note our fixture that inserts pins between the cam gears, locking them together at a "straight-up" position for torquing and installing the timing belt.

Vtec Dowel

noreply@blogger.com (Unknown) — Fri, 19 Feb 2010 11:27:00 +0000

Before the final installation of the cam caps, make sure to put the oil dowel and "O" ring in the head under the center cap. Yes, we lube the hell out of the camshafts.

Rocker Lube

noreply@blogger.com (Unknown) — Fri, 19 Feb 2010 11:26:00 +0000

We use moly-lube on the rocker arms, to insure that there will be as little friction as possible with the cam's new lobes. Keep observers will note that these rockers have been treated to new altered-radius wiper pads, which are furnace brazed to the rocker bodies and ground to work properly with the cams' lobes.

Clicking Clearance

noreply@blogger.com (Unknown) — Fri, 19 Feb 2010 11:25:00 +0000

If you look closely, you can see the heads of the exhaust valves behind the intakes in this photo. This particular head/valve/cam combination has .030" "clicking clearance". Sort of scary knowing that if one side is just a touch too quick, or too slow, the valves will lock and the engine will be history when the piston "closes" them.

Piston To Valve

noreply@blogger.com (Unknown) — Fri, 19 Feb 2010 11:24:00 +0000

It's also mandatory that you check piston to valve clearance with any non-stock combination you assemble. If you "assume" it'll be OK because you know of someone else running the combination, you're asking for trouble. I use the same fixture we use on the flow bench to place the indicator on the valve retainer.

Engineering workshop

Diesel Engine Combustion Efficiency

Measure Indicated Power in Diesel Engine with Indicator Diagram

Calculations

Now, Indicated Power of Unit [ip] =

Indicated Power of Unit = Pm L A N

Fuel Injector Testing

How Diesel Engines work

external electrical connectors broke/corroded

injector pintle doesn't fully seat on orifice

Body or mechanical joint leak in injector body

Injector windings don't lift pintle, seized pintle, or slow pintle cycling

Injector filters become clogged

Fuel Injectors Work

Engine speed governor

Crankshaft Bearing Failure

Maxi Fly Wheel

Trans Brace

Twin Disk cm

Header Flange

HDon't be mislead by the picture, but it's imperative that the header (and intake) gaskets do not hang in the way of the flow. If you don'eader Gasket

Hytech Header

Block Fittings

Balancer TDC Mark

Torquing Cam Bolts

Vtec Dowel

Rocker Lube

Clicking Clearance

Piston To Valve

Now, Indicated Power of Unit [i_p] =